9. Scalpellum

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_ Genus--SCALPELLUM. Pls. V, VI.

SCALPELLUM. Leach. Journ. de Physique, t. lxxxv, July, 1817. Q LEPAS. Linn. Systema Naturæ, 1767. POLLICIPES. Lamarck. Animaux sans Vertebres, 1818. POLYLEPAS. De Blainville. Dict. des Sc. Nat., 1824. SMILIUM (pars generis). Leach. Zoolog. Journal, vol. 2, July, 1825. CALANTICA (pars generis). J. E. Gray. Annals of Philosophy, vol. x, (new series,) Aug. 1825. THALIELLA (pars generis). J. E. Gray. Proc. Zoolog. Soc., 1848. ANATIFA. Quoy et Gaimard. Voyage de l'Astrolabe, 1826-34. XIPHIDIUM (pars generis). Dixon. Geology of Suffolk, 1850.

(Herm. et Foem.) Valvis 12 ad 15: lateribus verticilli inferioris quatuor vel sex, lineis incrementi plerumque convergentibus: sub-rostrum rarissime adest: pedunculo squamifero, rarissime nudo. (Herm. and Fem.) Valves 12 to 15 in number: latera of the lower whorl, four or six, with their lines of growth generally directed towards each other: sub-rostrum very rarely present: peduncle squamiferous, most rarely naked. Filamentary appendages, none: labrum, with the upper part highly bullate: trophi, various: olfactory orifices, more or less prominent: caudal appendages, uniarticulate and spinose, or none. Males, parasitic at or near the orifice of the sack of the female or of the hermaphrodite: thorax enclosed within a capitulum, furnished with three or four rudimentary valves, or with six perfect valves: peduncle either short and distinct, or confounded with the capitulum: sometimes mouth and stomach absent, and cirri non-prehensile; sometimes mouth and cirri normal.

Generally attached to horny corallines, in the warmer temperate seas over the whole world.

I have felt much doubt in limiting this genus: the six recent species which it contains, differ more from each other than do the species in the previous genera. Mr. Gray has proposed or adopted generic names for four of the species, and a fifth certainly has equal claims to this same rank. These genera have been founded almost exclusively on the number of the valves; and oddly enough, the numbers have generally been given wrongly, namely, in Scalpellum, Calantica, Thaliella, and Xiphidium. Scalpellum blends through S. villosum into Pollicipes; and this latter genus has an equal right with Scalpellum, to be divided into sub-genera, three in number. Hence, no less than eight genera might be made out of the twelve recent species of Scalpellum and Pollicipes, and their formation, in some degree, be justified; but, in my opinion, this inordinate multiplication of genera destroys the main advantages of classification. At one time, I even thought that it would be best to follow Lamarck, and keep the twelve recent species in one genus; but considering the number of fossil species, I believe the more prudent course has been followed, in retaining the two genera Scalpellum and Pollicipes; more especially as I can hardly doubt, that several other species will be hereafter discovered. Having so lately described in the Memoirs of the Palæontographical Society, the fossil species, I will not here further allude to them, than to state, that out of the fifteen species therein described, S. magnum comes very close to the recent S. vulgare, and that several Eocene and Cretaceous species, such as S. quadratum, S. fossula, and S. maximum, are allied to S. rutilum and S. ornatum. Scalpellum villosum, a recent species, has stronger claims than any other species to be generically separated; and its habits, in not being attached to horny corallines, are also different, but the identity of its Complemental Male with that of S. Peronii, and its numerous points of resemblance in structure with the other species, have determined me not to separate it. Scalpellum Peronii, villosum, and rostratum, in having a sub-carina,--in the rostrum being pretty well developed,--and in the Complemental Male being pedunculated, and furnished with a functional mouth and prehensile cirri, may be separated from S. vulgare, ornatum and rutilum; but even between these two little groups, S. rostratum is in some respects intermediate, namely, in having three pairs of latera, and more especially in the rudimentary condition of the valves of its Complemental Male, and in the position in which the male is attached to the hermaphrodite. The three species in the second little group, namely, S. vulgare, S. ornatum, and S. rutilum, are more nearly allied to each other in all their characters, especially in the characters drawn from their Males, than are the other three species. S. ornatum and S. rutilum are considerably nearer to each other than any other two of the species. Upon the whole I conclude that the six species must be thrown either into five or into four genera (the first three species making one genus), or all into one genus, and this latter has appeared to me the preferable course. The separation even of Scalpellum and Pollicipes, as already stated, is hardly natural. The fact of these genera having existed from a remote epoch, and having given rise during successive periods to many species now extinct, is probably the cause that the few remaining species are so much more distinct from each other, than is common in the other genera of Lepadidæ. Whenever the structure of the whole capitulum in the fossil species is well known, and as soon as more species, recent and fossil, shall have been discovered, then probably the genus Scalpellum will have to be divided into several smaller genera. Description.--The Capitulum is much compressed, and generally produced upwards; it is formed of from twelve to fifteen valves, which are rather thin, and with the exception of S. ornatum, almost entirely covered by membrane, bearing spines: the valves are seldom locked very closely together. A sub-rostrum exists only in S. villosum, which species leads on to Pollicipes; in S. vulgare the rostrum is rudimentary and hidden. The scuta, terga and carina, are much larger than the other valves: these five valves seem to differ essentially from the others in being at first developed under the form of the so-called primordial valves: the other valves commence by a small indistinct brown spot, very different from the hexagonal tissue of the primordial valves: I saw this very clearly in young specimens of S. vulgare. At first, the scuta, terga and carina, grow exclusively downwards (and permanently so in most fossil species), and therefore the growth of the scuta and carina is in an absolutely opposite direction to what it is in Lepas, Pæcilasma and Dichelaspis. After a short period the scuta are added to at their upper ends; the portion thus added, stands at a rather lower level, and projects in a rather different direction from the first-formed part of the valve, giving to it, in some respects, the appearance of having been broken and mended. This structure is common to S. vulgare, S. rostratum and S. Peronii. The upper Latera (except in S. villosum) grow in the same manner, namely, at first exclusively downwards, and then both upwards and downwards. The rostral and carinal latera (with the same exception of S. villosum) have their umbones seated laterally, at opposite ends of the capitulum,--the umbones of the rostral latera being close to the rostrum, and those of the carinal pair close to the carina, and consequently their chief growth is directed towards each other. The carina in all the species, except S. villosum, is either bowed or angularly bent; in the latter case the lower half is parallel to the peduncle, and the upper half, extending far up between the terga, is parallel to their longer axes. In some of the species the carina is added to almost equally at both ends; in S. ornatum it grows but little at the upper end, and to a varying degree in different individuals according to their age; in S. rutilum the umbo is at the apex, and there is consequently no upward growth; lastly, in S. villosum the carina widening much from the apex to the basal margin, grows exclusively downwards, and a portion of the apex projects freely,--characters all common to the carina in the genus Pollicipes. The upper latera occur in all the species; in the lower whorl there are either two or three pair of latera, in the former case the infra-median pair being absent. The latera differ considerably in shape in the different species. The Peduncle is generally rather short, and, with the exception of S. Peronii, is covered with calcified scales. These scales are generally small, and placed symmetrically in close whorls, in an imbricated order, with each scale corresponding to the interspace between two scales in the whorls above and below. In S. ornatum, the scales are so wide, transversely, that there are only four in each whorl. In S. villosum, the scales are spindle-shaped and arranged somewhat irregularly in transverse rows, not very near to each other. New calcareous scales originate only round the top of the peduncle, and they continue to grow only in the few upper whorls; and as the peduncle itself continues to increase in diameter by the formation of new inner membranous layers and the disintegration of the old outer layers, the calcareous scales come in the lower part of the peduncle to stand further and further apart. In the earliest stage of growth there are no calcareous scales on the peduncle in S. vulgare; they first appear under the carina. Spines are articulated in great numbers on the surface of the peduncle in S. vulgare, S. Peronii, and S. villosum, and very short ones on that of S. rostratum. Attachment.--All the species, except S. villosum, are attached to horny corallines: the singular means of attachment in S. vulgare will be described under that species, and is probably common to several of the other species. The larva in most, or in all cases, when it proceeds to attach itself, clings head downwards to the branch, and hence the capitulum comes to be placed upwards, with its orifice fronting the branch and the carina outwards. The sucking disc of the prehensile antennæ of the larva, in the five species examined, was a little pointed, and in shape resembled the hinder hoof of a mule: this may perhaps be accounted for by the narrowness of the branches of the corallines, to which it has to adhere: a large circular disc, as in Lepas, would have been worse than useless: the ultimate segment in most or all the species, has on its inner side (the segment being supposed to be extended straight forward) a notch or step, bearing, I believe, two spines. Size and Colour.--Some of the species attain a medium size, others are small. The valves are generally clouded red or pink, but sometimes white. Mouth.--The various parts vary far more than in any genus hitherto described. The labrum is highly bullate, with the upper part forming a rounded overhanging projection, and with the lower part much produced, so that the mouth is placed far from the adductor scutorum muscle, and consequently the orifice is directed more towards the ventral surface of the thorax than in most other Cirripedes: on the crest of the labrum there are some very small teeth in several of the species, but not in all. The mandibles have either three or four main teeth, generally with either one or two small teeth intermediate between the first and second large teeth, and in the case of S. Peronii, with small teeth between all the larger ones. The maxillæ have their edges furnished with many spines, and are either straight or have the inferior part prominent and step-formed. The outer maxillæ have the spines on their inner edges either continuous or divided into two groups, of which latter structure we have not hitherto had any very well characterised example. The olfactory orifices are either highly or moderately protuberant. In most of the species the prosoma is little developed, and the first cirrus is placed far from the second. The Cirri are generally but little curled, and have elongated segments, with long, generally serrated spines: the first cirrus varies in proportional length; the second and third cirri have both their rami more thickly clothed with spines than are the three posterior cirri, the spines being generally arranged in three or four longitudinal rows: the cirri, however, of S. villosum in all respects resemble closely the cirri of Pollicipes sertus and P. spinosus. The Caudal Appendages are uniarticulate, small, and clothed with spines: in S. villosum, however, differently from in all other allied forms, there are no appendages. The Stomach, in those species which I opened, is destitute of cæca. There are no filamentary appendages. Generative System. The ova are nearly spherical, and remarkably large, as was stated to be the case in the introductory discussion, in which the larva of S. vulgare, in the first stage of development, was described: the ovigerous fræna are small. The testes are large, but the vesiculæ seminales in some of the species extraordinarily small. Scalpellum ornatum, and perhaps S. rutilum, are unisexual; the other species are hermaphrodite, but most or at least some of the individuals, are furnished with Complemental Males. These latter are fully described under each species, so I will here only remark, that S. ornatum, which alone (excepting perhaps S. rutilum) is unisexual, has less claim than the other species to be generically separated: we have seen also, in Ibla, that similar sexual differences occur in two most closely allied species. It is very singular how much more some of the Males and Complemental Males in Scalpellum differ from each other, than do the female and hermaphrodite forms; this seems due to the different stages of embryonic development at which the males have been arrested. In the males, however, of S. rostratum, S. Peronii, and S. villosum, compared one with another, but not with the males of the other species, the parts of the mouth and apparently the cirri, resemble each other more closely, than do the same organs in the hermaphrodites. At the end of this genus I shall give a summary on the highly remarkable sexual relations both in Scalpellum and Ibla.

Distribution.--The species seem distributed over the whole world, but as far as we can trust our present scanty materials, are most common in the warmer temperate regions. The S. vulgare ranges from the Norwegian seas to Naples. Most of the species are inhabitants of deep water.

Affinities.--In the preliminary remarks, we have seen how this genus blends into Pollicipes; and under the head of Oxynaspis, I have shown its close affinity to that genus. If, indeed, we take Pollicipes spinosus, and destroy all but six of the already minute and almost rudimentary latera, we shall, as far as the capitulum is concerned, convert it into a Scalpellum, closely similar to S. villosum. If we take any species of Scalpellum, (excepting S. villosum and S. rutilum,) and destroy all the valves, but the scuta, terga and carina, we shall convert it into an Oxynaspis. Lastly, I have shown under Ibla, that in several most remarkable peculiarities of structure, there is a manifest affinity between Scalpellum and that genus. Geological History.--Full details on this subject have been given in the Memoirs of the Palæontographical Society. I will here only state, that the oldest known form of Scalpellum occurs in the Lower Green Sand. [=T= SUB-CARINÂ NULLÂ.] 1. SCALPELLUM VULGARE. Pl. V, fig. 15.

SCALPELLUM VULGARE. Leach. Encyclop. Brit. Suppl., vol. iii, 1824. LEPAS SCALPELLUM. Linn. Systema Naturæ, 1767. ---- Poli. Test. utriusque Siciliæ, Pl. vi., fig. 16. 1795. POLLICIPES SCALPELLUM. Lamarck. An. sans Vertebres, 1818. POLYLEPAS VULGARE. De Blainville. Dict. Sc. Nat., Plate, fig. 4. 1824. SCALPELLUM LÆVE, var. Leach. Zoolog. Journal, vol. ii, p. 215, 1825. ---- SICILIÆ, var. Chenu. Illust. Conch. Pl. iv, fig. 9. SCALPELLUM VULGARE, (et var.) Brown. Illust. of Conch., 1844, Pl. li., figs. 7 to 20.

S. (Herm.) valvis 14, si rostrum pæne rudimentale includatur: lateribus superioribus inæqualiter ovatis. (Herm.) Capitulum with 14 valves, including the rudimentary rostrum: upper latera irregularly oval. Mandibles, with four or five teeth: maxillæ, with the edge straight, bearing numerous spines. COMPLEMENTAL MALE flask-formed, with four rudimentary valves; no mouth; cirri not prehensile; attached to the occludent margin of the scutum, near the umbo.

Great Britain, Ireland, France, Norway, Naples. Attached to horny corallines, at from twenty to thirty, sometimes even to fifty fathoms in depth, according to Forbes and MacAndrew.

HERMAPHRODITE. Description.--Capitulum much flattened with the apex produced, of a pale brown colour, sometimes faintly tinted purple, composed of 14 valves, of which the rostrum is rudimentary and barely visible externally; valves thin, white, translucent, smooth, slightly marked by the lines of growth, separated from each other by rather wide interspaces of colourless membrane, which is thickly clothed by small, articulated spines of unequal length. The valves, excepting sometimes their umbones, are also covered with membrane, bearing spines, placed in rows parallel to the lines of growth; the spines are particularly numerous round the orifice of the sack. Scuta slightly convex, thrice as long as broad; upper part much acuminated; occludent margin almost straight; basal margin nearly at right angles to the occludent margin; the tergal margin is separated from the lateral margin by an angle more or less prominent; a slight curved ridge runs from the umbo to this angle, and this deserves especial notice, inasmuch as it indicates the outline which the valve assumed in its earliest growth, and which is permanently retained in most of the older fossil species. Along the occludent margin, there is a trace of a ledge, developed in a variable degree, and which is noticed only on account of the plainly visible ledge along this same margin, in the allied genus Oxynaspis. The umbo, or centre of calcification, is seated close to the occludent margin, and at about one fourth of the length of the valve from the apex. Internally, (fig. 15, a´, Pl. V,) the part above the umbo is flat; and beneath this upper part, there is a large rounded hollow (d) for the adductor muscle: a fold or indentation (a) running downwards from the umbo, extends in a very oblique line across the occludent margin. This fold is of high interest as giving lodgment to the Complemental Males, and will hereafter often be referred to. Terga, triangular, flat; occludent margin, very slightly arched. Carina much bent, with the umbo placed at barely one third of the entire length of the valve from the apex. Two very slight ridges can be perceived, one on each side, running from the umbo to the basal margin, and separating the roof from the parietes of the valve; these ridges are of great use in distinguishing the fossil carinæ of Scalpellum, from the carinæ of Pollicipes. The part above the umbo is formed by the upward production of a marginal slip along each side of the valve, which slips in the fossil species (C in the woodcut, fig. 1, given in the Introduction,) I have designated as the intra-parietes. The lower part of the valve gradually widens from the umbo downwards; internally, the whole is deeply concave, and continuously curved. The angle varies at which the upper and lower portions externally meet each other; but is never less than 135°. The upper part of the carina runs up between the terga for three-quarters of their length; the basal margin does not extend down low enough to pass between the carinal latera. Rostrum, (fig. 15 b´, seen externally, and highly magnified,) minute, almost hidden by the enveloping membrane and by the small prominent umbones of the rostral latera; in area equalling about one fourth of the rostral latera; externally pyramidal, with the upper side rather longer than the lower; internally slightly concave, square, with the upper margin and sometimes with the lower margin, slightly hollowed out. Umbo of growth nearly central. Upper Latera, flat, irregularly oval, with an almost rectangular shoulder under the basal angle of the terga; in area, about one third larger than the largest valve of the lower whorl; the exact degree of elongation of the oval figure varies a little. Umbo seated a little above the central point. Lower Whorl,--Rostral Latera, nearly twice as long as broad, lying under the basal margins of the scuta: umbo seated over the rostrum; opposite end, towards which the valve widens either sensibly or but little, is either square or rounded; in area, less than any of the other valves, excepting the rostrum; in breadth, equalling either half or one third of the height of the infra-median latera; growth, directed chiefly towards the infra-median latera. The freely-projecting umbo is about one sixth part of the entire length of the valve. Infra-median Latera, rather larger than the carinal latera; their shape varies from elongated pentagonal with the angles rounded, to oval, with the longer axis directed upwards. The umbo is seated a little above the middle of the basal margin, so that there is some little growth downwards, but the main growth is upwards. The upper point generally stands a little above that of the carinal latera. Carinal Latera, flat, less in area than the infra-median latera; basal margin nearly straight; carinal margin slightly hollowed out, terminal margin arched and protuberant. The umbones of the two valves almost touch each other under the middle of the carina; main growth towards the infra-median latera and upwards; umbones projecting not above one fifth of the entire length of the valve. Peduncle, much flattened, rarely as long as the capitulum, with the upper end nearly as wide as it; the lower end is either blunt, or tapers to a very fine point. The calcareous scales are transversely elongated, and are about four times as wide as high; their internal surfaces are slightly concave, and their external, convex; the two ends are pointed. Viewed internally, the scales approach in shape to rhomboids. There are, in a medium-sized specimen, about twenty scales in each whorl, their tips overlapping each other: the whorls are placed not very near each other and at rather unequal distances, except round the uppermost part, where, being in process of formation, they are packed closely together. The membrane uniting the scales, supports numerous transverse rows of articulated spines, varying from 1/100th to 1/500th of an inch in length, and each furnished with a long sinuous tubulus, 1/10,000th of an inch in diameter, running through the membrane to the underlying corium. Attachment.--Specimens are attached to various horny corallines, and occasionally to the peduncles of each other.[51] In both cases, supposing the coralline to be erect, the capitulum is placed upwards, with its orifice towards the branch to which it is attached, and consequently with its carina outwards. Where several are crowded in a group, their peduncles often become twisted and their positions irregular, with their orifices facing in any direction. This uniform position is simply the consequence of the larva attaching itself head-downwards, and from the position of the prehensile antennæ, necessarily with its sternal surface parallel and close to the branch of the coralline; hence the dorsal surface, which afterwards is converted into the carina, faces outwards. The peduncle, as already stated, often tapers, at its basal extremity, to a sharp point. In very young specimens, for instance in one with a capitulum only 1/20th of an inch in length, the method of attachment is the same as in Lepas and many other genera, namely, by cement proceeding exclusively from the antennæ of the larva; but in older and full-grown specimens, instead of the whole bottom of the peduncle becoming flattened and broadly attached, which would be here impossible, the cement is poured out through a straight row of orifices along the rostral edge, thus causing, by an excellent adaptation, a narrow margin to adhere firmly to the thin and cylindrical branches of the coralline. These orifices are represented, magnified seven times, in Pl. IX, fig. 7, in which the lower attached portion of the peduncle is split open and exhibited; they are circular, and stand at regular intervals, in a straight line; the higher orifices are larger, but further apart from each other than the lower ones; in one full-grown specimen, I counted ten of these orifices in a length of exactly a quarter of an inch. At each period of growth, the corium recedes a little from the attached portion of the peduncle; of which portion, the greater part is thus left empty and as incapable of further growth, as are the larval antennæ at the extreme point: in the specimen figured, the corium extended a little below the upper orifice. The prehensile antennæ, however, I must remark, do not strictly rise from the extreme point of the peduncle, but at a little distance from it, on the rostral surface; this simply ensues from the antennæ in the larva, being situated on the sternal surface, close to, but not actually on the front of the head. The two cement glands are seated high up on the sides of the peduncle, and remote from each other; they are small, unusually globular and transparent. The two cement-ducts (fig. 7 a a) proceeding from them, are 3/2000ths of an inch in diameter, and run in a zig-zag line; at the point where they pass through the corium to enter the lower attached portion of the peduncle, they become closely approximated, and partially imbedded in the membrane of the peduncle. Together they run along the rostral edge, giving out through each orifice a little disc of brownish cement, and finally they enter the larval antennæ. The peduncle, just above the attached portion, where still lined by corium, no doubt increases in diameter at each period of growth, and must, I presume, become pressed against the almost parallel branch of the coralline. The corium, at this same period, shrinks, or is absorbed, and the two cement-ducts come in contact with, and adhere to, the inner surface of the outer membrane of the peduncle; and then, by a process which I do not understand in this or any other Cirripede, apertures are formed both in the ducts and through the membrane, so that the cement passes through, firmly fastening the outer surface of the peduncle with its calcareous scales and spines, to the coralline.

[51] Mr. Peach, (Transact. Brit. Assoc., 1845, p. 65,) states that this is sometimes the case in Cornwall; and I have seen a similar instance in a fine group from Naples.

The structure of the larval prehensile antennæ will be most conveniently described when we come to the Complemental male; and figures (10-12, Pl. V) will be given. Size and Colours.--Montagu states ('Test. Brit.,' p. 18) that British specimens rarely have a capitulum .62 of an inch in length; I have, however, seen an Irish specimen, .7 long; and several specimens, from the Bay of Naples, .8 long, and including the peduncle, 1.3 in length. The valves in all the specimens are white, and the membrane connecting them either nearly white, or dirty pale yellowish, or purplish-brown. Within the sack the corium under the valves is tinted pale purple, and two very faint bands of the same colour can generally be distinguished running down the two sides of the peduncle. Body, coloured yellowish-white, with the upper segments of the pedicels of the cirri, tinted in front with purple. Body, much flattened, the prosoma is very little developed; the mouth placed far from the adductor muscle, and is directed in a remarkable manner towards the ventral surface of the thorax: the first pair of cirri stands far separated from the second pair. Mouth.--Labrum with the upper part highly bullate, forming an overhanging projection equalling the longitudinal axis of the mouth; basal margin much produced; crest with a row of bead-like teeth. Palpi rather small, with their external margin straight, and internal margin oblique: the bristles on the two palpi just meet each other. Mandibles, with five or six teeth, with the second, (or second and third, when there are six teeth,) smaller than the others; in two specimens, there were five teeth on one side and six on the other; inferior angle rather broad and strongly pectinated. Maxillæ with the edge nearly straight, without any notch, but with the inferior portion very slightly projecting; there are twelve or thirteen pairs of unequal spines, of which some of the middle ones are rather longer than the others, and almost as long as the two upper great spines. Outer Maxillæ.--On the inner margin the bristles are divided into two separate tufts; exteriorly, near the base, there is a distinct rounded swelling with bristles. The olfactory orifices are highly protuberant, approximate, flattened, scarcely tapering towards their upper ends. Cirri.--The five posterior pair are elongated, very little curled, with short pedicels; their segments are long, not at all protuberant in front, bearing five or six pairs of long, slightly serrated spines, with a very minute tuft of bristles between each pair, and with some short lateral spines on the inner side of each segment; on the fourth pair of cirri, these lateral spines are considerably developed; dorsal tufts consist of fine spines, with one much longer than the others. First pair short, separated by a wide interval from the second; rami unequal in length, by between two and four segments; longer ramus having nine segments, scarcely half as long as the rami of the second cirrus; shorter ramus with seven segments; in the same individual there were twenty segments in the sixth cirrus. The segments in the shorter ramus of the first cirrus are oblong in a transverse direction, and may be compared to a set of shields placed transversely and strung together; in the longer ramus the segments are longitudinally oblong; in both they are thickly covered with spines. Second cirrus; the anterior ramus is a little broader than the posterior ramus, with the segments bearing about five rows of bristles; fifteen segments in the shorter ramus. Third pair, with the two rami equal in thickness, and with the segments differing very little from those of the posterior cirri, excepting that the serrated spines in the external lateral rows are rather larger. The fourth pair is remarkable by having, on the inner side of the upper edge of each segment, a little tuft of minute smooth spines, flattened, and a little enlarged near their ends, so as to be spear-shaped; I could not see these singular spines on the other cirri. The lower segments of the pedicels of all the cirri, excepting the sixth pair, are remarkable from having their inner edges, in the middle, produced into a considerable, abrupt, rounded projection, irregularly covered with spines. Caudal Appendages, (Pl. X, fig. 21,) very small, flattened, of nearly the same width throughout; in a medium-sized specimen, only 1/100th of an inch in length; each bears from ten to twenty small bristles placed distantly from each other, of which those on the rounded apex are the longest. Generative System.--The penis is remarkably acuminated; the vesiculæ seminales are unusually small, and enter only for a short distance into the prosoma; the testes are large. The ovarian tubes are of large diameter; the ova are nearly spherical and large, namely, 9/400ths of an inch in diameter; they are not numerous, and lie in single layers in the two lamellæ. The ovigerous fræna are well developed, and lie under the scuta; one I measured was 5/100ths of an inch in length and 2/100ths in width; the margin is obliquely truncated and slightly sinuous. This species breeds late in the autumn, and even in mid-winter; I have examined a specimen from Cornwall with ova containing larvæ, taken on the 26th of October; again, in another specimen from Belfast, sent to me by Mr. Thompson, taken in January, there were ova in the lamellæ, and therefore no doubt impregnated; and on February the 12th I received from Mr. Peach, from Cornwall, specimens so very young that they must have become attached during the first days of the month. Varieties.--The specimens from near Naples, (which I owe to the kindness of the Rev. F. W. Hope,) are somewhat larger, and differ slightly from those of Britain: they form, I imagine, the S. Siciliæ of Chenu. After carefully examining them internally and externally, I think it is quite impossible to consider them specifically distinct, for although in several specimens, the valves were placed a little further apart from each other,--the upper latera a little more elongated,--the carinal latera rather narrower in their upper half,--the infra-median latera rather more rounded,--and, lastly, in the scuta, the tergal margin extended almost in the same line with the lateral margin; nevertheless in other specimens, I could perceive no difference whatever. It is, however, remarkable that in several full-grown Neapolitan specimens there were no Complemental males, whereas I have never seen a single full-grown British specimen without such being present. In some specimens in the British Museum, without any given locality, I have observed considerable variation in the breadth of the carinal and rostral latera. COMPLEMENTAL MALE. Pl. V, figs. 9-14. When first dissecting Scalpellum vulgare, I was surprised at the almost constant presence of one or more very minute parasites, on the margins of both scuta, close to the umbones: these are represented, but rendered darker and therefore more conspicuous than in nature, in the drawing, Pl. V, fig. 15, which is three times the natural size. I carelessly dissected one or two specimens, and concluded that they belonged to some new class or order amongst the Articulata; but did not at that time even conjecture, that they were Cirripedes. Many months afterwards, when I had seen in Ibla, that an hermaphrodite could have a complemental male, I remembered that I had been surprised at the small size of the vesiculæ seminales in the hermaphrodite S. vulgare, so that I resolved to look with care at these parasites; on doing so, I soon discovered that they were Cirripedes, for I found that they adhered by cement, and were furnished with prehensile antennæ, which latter, I observed with astonishment, agreed in every minute character, and in size, with those of S. vulgare: the importance of this agreement will not at present be fully appreciated. I also found, that these parasites were destitute of a mouth and stomach; that consequently they were short-lived, but that they reached maturity; and that all were males. Subsequently the five other species of the genus Scalpellum were found to present more or less closely analogous phenomena. These facts, together with those given under Ibla (and had it not been for this latter genus, I never probably should have even struck on the right track in my investigation,) appear sufficient to justify me, in provisionally considering the truly wonderful parasites of the several species of Scalpellum, as Males and Complemental Males. When these parasites are fully described, will be the proper time to discuss and weigh the evidence on their sexual relations and nature. I will now describe the parasite of S. vulgare. General Appearance.--Shape, flask-like, compressed (Pl. V, fig. 9, magnified 36 times), with a short neck: the outline is usually symmetrical, but sometimes is a little distorted on the under side. The creature is imbedded more than half its length or depth in the transparent, spine-bearing chitine border of the scutum of the hermaphrodite. Its length, or longer axis, varies from 10 to 11/400ths; its breadth, or transverse axis, is 6 to 7/400ths; and its thickness, for it is much flattened, is only 4/400ths of an inch. On the summit, there is a fimbriated orifice (a), the size of which can rarely be made out quite distinctly, owing to the extreme thinness of the membranous edges. A little way beneath the orifice, there are four little blunt, bristly points (b), generally rather more than the 1/1000th of an inch in length; they are rather variable in size, and seem to be of no functional importance; directly beneath them, there are four little calcareous beads (as may be known by their dissolving with effervescence in any acid, and breaking easily under the needle); these are the 3/2000ths of an inch in their larger external diameter; they are rather deeply imbedded in the outer integument, and taper a little downwards ending in a concave terminal point, into which a minute tubulus enters, like those passing into and through the valves of ordinary Cirripedia: along the axis of imbedment, they are often 4/2000ths of an inch in length. These calcareous beads or rudimental valves are seated in pairs, at the two ends of the flattened animal, so that when the animal is laid on one side, the upper bead in each pair exactly covers and hides the lower one. The outer integument is composed of chitine, as may be inferred from boiling caustic potash having no effect on it; the upper part is thicker than the imbedded portion and is wrinkled transversely; it is covered with minute spines 4/10,000ths of an inch in length, either single or in groups of two and three, (Pl. V, fig. 14.) This outer tunic is lined by corium, sometimes slightly mottled with dull purple; and this by delicate, longitudinal, striæ-less muscles, running from the base up to the under edge of the orifice; these longitudinal muscles are crossed, at least, in the upper part, by still finer transverse muscles. Thorax and Abdomen.--When the external integument is cut open, the thorax (Pl. V, fig. 13) is found lodged within an inner sack or rather tube, extending from near the bottom of the animal, up to the external orifice. The whole thorax is sometimes forced through the orifice, owing perhaps to the action of the spirits of wine and consequent endosmose, and is thus well displayed without dissection. The thorax tapers a little, is much flattened and straight; its length, together with the terminal abdominal lobe, is about 6/400ths of an inch; it is formed of very thin, most finely hirsute membrane, transversely wrinkled and so extensible, that when everted by the internal muscles being seized, it stretches to twice its former length; in this condition, five transverse articulations are displayed. The abdominal lobe is smooth, and cannot be stretched, or turned inside out by pulling the above muscles. On the thorax, corresponding with the interspaces between the five transverse articulations, there are four pair of short limbs, but their bases, I believe, are prolonged across the inner or ventral surface of the thorax, so as almost to touch each other. These limbs, I believe, have no articulations, except, perhaps, where united to the thorax. The anterior or lowest limb, on each side, supports two or sometimes only a single spine; this pair is rather smaller than the second, and is placed a little more distant from it, than are the upper pairs from each other. The second pair differs from the upper two, only in having its three spines a very little shorter. The two upper or posterior pair exactly resemble each other; each has two spines on the summit, and a third seated lower down, on a little notch on the outer side, but with its point on a level with the others. The points of the spines of the two upper limbs, stand on a level with the external spines at the end of the abdomen. All the spines are of excessive tenuity and sharpness; they are straight, long, and not plumose. The abdominal lobe is square, and from not being wrinkled, has a different appearance from the thorax: on each of the posterior angles, there are three moderately long, very sharp spines, with the tips of the outer pair bent a little inwards; in the middle between them, there are two little spines, and a little below and outside these latter, on the ventral surface, there are two other longer spines with their tips bent inwards; and again, lower down, two other pair, one beneath the other, of short spines. Perhaps, the three pair of spines on the ventral surface, mark the three segments, which are distinct on the abdomen of the larva in the last stage of its development, in Lepas and other genera. In the same way, it is probable that the lateral spine on the notch in each limb, marks the point where, in the larva, there is an articulation. Altogether, there are seven pairs of spines on the abdomen, and eleven pairs on the thoracic limbs. A little way beneath the lower or anterior pair of limbs, the thorax is abruptly bent, and becomes confluent with the lower internal parts of the whole animal. Here, the very delicate membrane of chitine which lines the sack or tube, extending from the external orifice, can be seen to be continuous, as in all Cirripedes, with the outer tunic of the thorax. Within the thorax, there are some longitudinal muscles, without transverse striæ, which, I believe, enter the short limbs, but not the abdomen, as I infer from the latter not being everted when they are pulled. At their lower ends these muscles terminate abruptly, and from being contracted are often a little enlarged. They extend a short way beneath the lower pair of limbs, and are, I suspect, attached to the outer integument of the animal, near the base. After the most careful dissection of very many specimens, and their examination in many different methods (as by caustic potash, &c.), I can venture positively to assert that there is no vestige of a mouth, or masticatory organs, or stomach: I did not see any anus, but I will not affirm that such does not exist. In the upper part of the animal, lying under the superficial muscles, and close beneath the upper line of their attachment, I found in all the specimens, an eye, of a pointed oval form, rather less than 11/12,000ths of an inch in diameter, formed of an outer capsule, lined with purple pigment-cells, and surrounding, as it appeared, a lens. The eye is not introduced in fig. 9, for I could not see it, except by dissection, and therefore do not know its exact relative position. Generative System.--The contents of the animal, between the sack containing the thorax and the outer integuments, and directly under the thorax, varied much in condition: in young and lately attached specimens the whole consisted of a pulpy mass with numerous oil-globules; in other specimens, apparently more mature, there were vast numbers of cells, sometimes cohering in sheets, about 3/10,000ths of an inch in diameter, and having darkish granular centres; these I believe to be the testes, for in a specimen presently to be mentioned, in which the vesicula seminalis was gorged with spermatozoa, I found adhering to its outside, a mass of cells of exactly the same diameter, but now empty and transparent instead of having brownish centres. Lastly, in several other specimens, at the very bottom of the sack-formed animal, there was a brownish, pear-shaped bag, of different sizes in different individuals, and occasionally broader even than the thorax. This bag contained either pulpy matter, or a great mass of spermatozoa. Before being disturbed, these spermatozoa lay parallel to each other in flocks, and they yielded to the needle in a peculiar manner, so that I found (having had experience with these bodies in living Cirripedia) I could almost tell before examination under the compound microscope, whether or not I should see spermatozoa. Many had distinct heads,[52] which were two or three times as broad as the filamentary bodies; the latter when placed between glass were the 1/20,000th of an inch in diameter. I compared these spermatozoa with others taken out of the vesiculæ seminales of the individual hermaphrodite S. vulgare, to which the parasite was attached, and could not perceive the slightest difference in them. The brownish pear-shaped bag, or vesicula seminalis, the coat of which seems fibrous, could sometimes be distinctly traced, sending a chord or prolongation far up the thorax: at the end of the abdominal lobe, no doubt there is an orifice; and this, I believe, I once distinguished. Owing to this chord, the bag often adheres to the thorax, when the latter is dissected out of the general integuments; in this condition, I twice clearly made out that it was single: in one other specimen, however, there appeared to be two small vesiculæ seminales. By using a condenser and very brilliant light, the outline of the vesicula seminalis could sometimes be distinguished before dissection, at the bottom of the sack-formed animal; and such was the case in the specimen drawn in fig. 9.

[52] I do not understand the development of the spermatozoa in Cirripedia: in a recent Chthamalus and Balanus, I found the greater number had a little filament in front of the head or nodular enlargement, which latter varied in size and in shape from globular to that of a spindle. The filament before the head, also, varied in proportional length; it did not project in exactly the same straight line with the hinder part, and some of the spermatozoa were entirely without this filament in front;--such is the case with the spermatozoa here described.

Although I have dissected, at least, thirty specimens, taken at different times of the year, and from different localities, and when many of the specimens were mature and ready for the impregnation of ova, as clearly shown by the presence of innumerable spermatozoa, I have never seen even a trace of an ovum or ovaria. Antennæ and Attachment.--The prehensile antennæ (Pl. V, fig. 10), are seated a little above the very base of the sack-like animal; and this might have been expected from the antennæ in the larva, being seated on the ventral surface, not at the very extremity of the head. By a very strong light, they can sometimes just be seen whilst the parasite is attached to the hermaphrodite (the scutum of the latter having been cleaned on the under side), and are thus represented in fig. 9. They are formed of thicker membrane than the general integument of the body: the second segment, or disc, is pointed and hoof-like; when seen in profile (fig. 11), the upper convex surface has a uniform slope with the upper surface of the basal segment; it is furnished with a single backward pointing spine, attached, I believe, on the under side, nearly opposite the articulation of the ultimate segment: at the apex, there are some excessively minute hairs or down. The ultimate segment projects rectangularly outwards as usual, and has on its inner side, rather beneath the middle, a conspicuous notch (fig. 12), which bears two or three long, non-plumose spines; on the summit there are three or four rather shorter spines. On the outside of the great basal segment there is a single spine curving backwards. The importance of the following measurements (in fractions of an inch) will hereafter be seen.

 
  Length of whole organ, from end of disc to the further   }
  margin of the oblique basal articulation                 } 38-39/6000

  Length of whole organ, to the inner margin of the oblique}
  basal articulation                                       } 1/6000

  Breadth of basal segment, measured half-way between the  }
  basal and second articulations,--the limb being viewed   }
  from vertically above                                    } 8/6000

  Length of hoof-like disc, measured from the apex to the  }
  middle of the articulation with the basal segment        } 9-10/6000

  Breadth of ditto                                           5/6000

  Length of ultimate segment                                 6/6000

  Breadth of ultimate segment beneath the notch              7/20000

  Breadth of ultimate segment above the notch                5/20000

I did not see the cement-ducts, which, perhaps, was owing to the corium extending from the inside of the whole animal some way into the antennæ, thus rendering them rather less transparent than in common Cirripedes. That the ducts and cement-glands exist, is certain, for the antennæ in every case were enveloped in a little irregular mass or capsule of the usual, brown, transparent, laminated cement. When several of these parasites were attached close together, the cement ran up between them. I may here state, that I found on one Scalpellum, three males very lately attached, and not as yet imbedded in the chitine border; they were white, opaque, pulpy, and full of oily globules; the lower part was considerably more pointed, and extended further beyond the prehensile antennæ, than in the older and imbedded specimens. There were distinct remnants of two great reddish-brown eyes, showing that in this respect the larvæ of the male in their last stage of development, are characterised like the larvæ of other Lepadidæ. The male larva would, probably, be a little larger than the male itself; but yet compared with the larva in the earliest stage, there can have been unusually little increase of size during the several intermediate metamorphoses; I judge of this from the dimensions of the larva of the hermaphrodite in the first stage, namely, 9/400ths of an inch, exactly the size of some of the smaller males. In the allied genus Ibla, the increase is also less than is usual, namely, from 15/1000ths of an inch, the diameter of the ovum, to only 25/1000ths of an inch, the length of the boat-shaped larva, just before its final metamorphosis. Habits and Concluding Remarks.--The males are imbedded in the spinose chitine border of the occludent margin of the scuta, exactly over an oblique fold or notch (fig. 15 _á a), close by the umbo. This fold has no direct relation to the males, but being present is taken advantage of by them; for it occurs in the young hermaphrodite, before the attachment of the males, and in species of the genus in which the males are attached to other parts. It occurs, also, in fossil species of Pollicipes, and in these it seems caused by the upper inner part of the valve being rendered more and more prominent during growth: in the present species, I suspect, its origin is connected with the formation of a ridge bounding the outer side of the pit for the adductor scutorum muscle: we shall see in the next species, that this fold is of the highest importance in relation to the position of the Males. The transparent chitine border of the scuta is broad, and fills up the fold in the shell, so that the outline of the occludent margin is not affected by it: in the drawing (fig. 9) some of the inner layers of chitine (e e), which dipped into and filled up the fold, have been removed, that the lower part of the animal might be more plainly exhibited. The chitine bears numerous spines of various lengths, which must afford some protection to the males, rudely arranged in lines, parallel to the edge of the valve, indicating the successively-formed layers of chitine; each spine has a fine, tortuous tubulus connecting its base with the underlying corium. The extreme outer edge of the border is thin, forming a kind of lip, close beneath which the delicate tunic lining the sack is attached. During continued growth, the valve is added to in thickness, and so is the chitine border, and likewise in breadth. It appears that the larva of the male must attach itself on the under side of this border, on the edge of the tunic of the sack, and that by the action of the cement, the corium beneath is killed (as I believe always is the case with other parasitic Cirripedia), whereas on both sides, the chitine continues to be added to, so that the male, excepting the upper and always projecting portion, becomes imbedded at first laterally, and ultimately all round: I have seen specimens in several different stages of imbedment. Hence, in old specimens, with a thick and broad chitine border, it might and does come to pass that one male is imbedded (the valve being laid flat) directly beneath another. I have examined a great number of specimens from various localities, taken at different times of the year,--some dozen specimens from Cornwall,[53] and several from unknown localities in various collections; some from Ireland, from the Shetland Islands, from Norway, and from near Naples. Every one of these specimens, with the exception of some of the Neapolitan ones, had parasitic males attached to them: I must also except very young specimens, on which they never occur. On a Cornish specimen, with a capitulum a little more than one fifth of an inch in length, it may be mentioned as unusual that there were three males. In young specimens there is generally one male on each scutum, but sometimes there are two, and sometimes none on one side. In large old Cornish specimens I have counted on the two sides together, six, seven, and eight males, and in one Irish specimen no less than ten, seven all close together on one valve and three on the other, but I do not suppose that all these were alive at the same time. In the Neapolitan specimens, however, which are the largest that I have seen, there was in no case more than two; and out of seven or eight specimens, four had not any male; so that it would appear there is something in this locality hostile to the development of the parasitic males. I have noticed only one instance (that given in fig. 9) in which the males were imbedded a little way apart; generally they touch each other, and are cemented together: where there are several males, they occur at different levels, as measured from the under or upper surface of the chitine border: in one instance of four males adhering to one valve, I distinctly perceived that the lowest one was white, pulpy, and recently attached; the two above, which were placed close together and between the same laminæ of chitine, were mature; and the third still higher up, was dead, empty, transparent, and half decayed: in some other instances, I have found the uppermost parasites dead, and, together with the surrounding chitine, partially worn away.

[53] I am greatly indebted to Mr. Peach for his unwearied kindness in procuring me fresh specimens. Mr. W. Thompson allowed me to dissect one, possessing particular interest, out of his three Irish specimens. Professor Forbes procured me a specimen from the Shetland Islands, and Professor Steenstrup was so kind to take pains to send me some Scandinavian specimens.

The larva of the male must have a different instinct from the larva of the hermaphrodite; for the latter attaches itself head downwards to a coralline, whilst the male larva crawling on the scuta of the hermaphrodite, discovers, I presume by eye-sight, the fold in the shell beneath the translucent border of chitine, and there invariably attaches itself. Its object in choosing this particular spot, I believe, simply is that the depth or thickness of the chitine is there greater, and sufficient for its imbedment, which would hardly be the case elsewhere. This parasite has, as we have seen, no mouth or stomach, and indeed, considering its fixed position and the non-prehensile condition of its limbs or cirri, a mouth would have been of no service to it, without it had been extraordinarily elongated. The male must live on the nourishment acquired during its locomotive larval condition; and its life no doubt is short, but yet not very short, as I infer from the depth to which mature specimens are buried in the chitine border. The full development of the spermatozoa consumes, I suppose, some considerable lapse of time. The thorax and limbs, though furnished with muscles, are obviously, as already remarked, of no use for prehension; these parts serve, probably, to defend the little creature, when its eye announces the passing shadow of some enemy, and for this purpose they are well adapted from the extreme sharpness of the spines. The thorax, into which I traced the vesicula seminalis, no doubt also serves for the emission and first direction of the spermatozoa; and hence, perhaps, its singularly extensible structure. I have already remarked, that in specimens preserved in spirits, the thorax is often largely protruded, and bent down at right angles to the orifice. I presume this is caused by endosmose; nevertheless it deserves notice, that it was in these protruded specimens that the vesicula seminalis was most conspicuously gorged with spermatozoa. I suspect the longitudinal and transverse muscles lining the upper part of the outer integuments of the whole animal, can be of little use to the creature, without it be to aid in the protrusion of the thorax, and perhaps in the violent expulsion of the spermatozoa, thus causing them to reach the ovigerous lamellæ within the sack of the hermaphrodite. It is also probable, that the action of the cirri of the hermaphrodite, would tend to draw inwards the spermatozoa in the right direction. In one specimen, the spermatozoa in the hermaphrodite and in the male were mature at the same time; in another this was not the case; and as the males, apparently, become attached at all periods of the year, this want of coincidence in maturity must often occur. Can the males retain their spermatozoa, till told by some instinct, that the ova in the sack of the often fecundated hermaphrodite are ready for impregnation; or are the spermatozoa sometimes wasted, as must annually happen with such incalculable quantities of the pollen of many dioecious plants? This little Cirripede is, in many respects, in a partially embryonic condition. There is no separation between the capitulum and peduncle; there is no mouth; and the thorax, throughout its whole width, opens into the anterior part of the animal: the limbs differ greatly from those both of the mature Cirripede and of the larva, but come closest to the latter: the preservation of the abdomen is a well-marked embryonic character. On the other hand, the four rudimentary calcareous valves, the narrow orifice, the hirsute outer integument, the two muscular layers, the single eye, and male internal organs, are all characteristic of the fully-developed condition. The four little valves, as I believe, represent the scuta and terga, though they are placed considerably below the orifice: the little bristly points have no homological signification, and are absent in the male of the following closely allied species. The four pairs of limbs answer to the four posterior cirri, as may be inferred from their proximity to the abdominal lobe, and from the three posterior pairs closely resembling each other, and differing a little from the first pair; this latter pair corresponds with the third pair in the hermaphrodite form of Scalpellum. If I am right in believing that only a single vesicula seminalis is ordinarily developed in the male, this is a special and singular character. As stated in the beginning of this description, from the one great fact of the absolute correspondence of the prehensile antennæ of the parasite, with those of the hermaphrodite Scalpellum vulgare, together with its fixed condition, its short existence, and exclusively male sex, I have thought myself justified in provisionally considering it as the Complemental Male of the Cirripede to which it is attached; but I hope final judgment will not be passed on this view, until the whole case is summed up at the end of the genus.[54]

[54] I trust, before long, that some naturalist, with more skill than I possess, will examine these parasites on Scalpellum vulgare, which unfortunately is the only species of the genus that can be easily obtained. Fresh specimens, or those preserved in spirits of wine, are necessary. The action of boiling caustic potash is very useful in cleaning the prehensile antennæ. If these latter organs are sought in the hermaphrodite for the sake of comparison, young specimens, adhering to clean branches of a coralline, should be procured, and caustic potash used.

2. SCALPELLUM ORNATUM. Pl. VI, fig 1.

THALIELLA ORNATA. J. E. Gray. Proc. Zoolog. Soc., 1848, p. 44, Annulosa, Plate.

S. (Foem.) valvis 14, sub-rufis: lateribus superioribus quadranti-formibus, arcu crenâ profundâ notato. (Fem.) Capitulum with 14 reddish valves: upper latera quadrant-shaped, with the arched side deeply notched. Mandibles with three teeth; maxillæ narrow, bearing only four or five pair of spines. MALES, two, lodged in cavities on the under sides of the scuta; pouch-formed, with four unequal, rudimentary valves: no mouth: cirri not prehensile.

Algoa Bay, South Africa. Attached to Sertularia and Plumularia. British Museum.[55] [55] I am greatly indebted to Mr. Bowerbank for specimens of this extremely interesting species; also to Mr. Morris, to whom Mr. Bowerbank had given some of the original specimens.

FEMALE. Capitulum oblong, with the upper portion much produced; valves, 14, thick, naked, closely locked together, irregularly clouded with pale crimson; the membrane connecting the valves is not furnished with spines. On most of the valves there are furrows and ridges diverging from the umbones, and the lines of growth are plainly marked: in the valves of the lower whorl, the umbones are slightly protuberant. Scuta, convex, unusually thick, oblong, quadrilateral, with the occludent margin the longest; lateral margin slightly hollowed out. The umbo (and primordial valve) is situated at the uppermost point of the valve, and consequently the growth is exclusively downwards. On the under side (Pl. VI, figs. 1 b´ and 1 c´), in about the middle of the valve, there is a pit (a) for the adductor scutorum muscle, the depth and distinctness of which varies a little; above the pit, and between it and the apex, there is a transverse, oblong, deeper depression (b), within which, the male is lodged. A small portion of the apex of the valve projects over the terga. Terga, large, nearly equalling the scuta in area, flat and sub-triangular; the scutal margin is not quite straight. The apex of the valve is thick and solid, and must have projected freely for a length equalling one third of the occludent margin. Carina, laterally broad, angularly bent; slightly widening from the apex to the base; internally, deeply concave. The position of the umbo varies, in young specimens it is seated at the uppermost point, and consequently in such there is no upward growth; in older specimens, from the junction and upward production of that part on each side of the valve, which I have called in fossil specimens the intra-parietes, the valve is added to above the umbo, but to a lesser degree than in S. vulgare. Slight ridges separate the roof from the parietes, and the parietes from the intra-parietes. Rostrum, minute, narrow, widening a little from the apex downwards, inserted like a wedge between the umbones of the rostral latera, and hardly projecting above their upper margins, so as to be easily overlooked: internally concave. Upper Latera (fig. 1 _á), quadrant-shaped, with a deep square notch cut out of the arched margin, which notch receives the upper point of the carinal latera; the surface of the valve between the notch and the umbo is depressed.[56] Rostral Latera, small, gradually widening from the umbo to the opposite end, which is obliquely rounded. Infra-median Latera, approaching to diamond-shaped, placed obliquely to the longer axis of the capitulum; or the upper part may be described as spear-shaped.

[56] The only valve which I have seen at all like this, is a fossil specimen from the Upper Chalk of Scania; this is described in my memoir on the Fossil Lepadidæ (Palæontographical Society), under the name of Scalpellum solidulum (Tab. 1, fig. 8, e, f), and is perhaps erroneously there considered as a carinal latus.

Carinal Latera: these appear as if formed of two valves united together; the upper portion, widening as it ascends in a curved line, terminates in a rounded margin, which enters the deep notch in the upper latera; the other and lower portion is shorter, and terminates in a square margin abutting against the infra-median latera; the umbones of the carinal latera project beyond the line of the carina. Direction of the Lines of Growth in the Valves.--This should always be carefully observed, on account of the great diversity there is in this respect between the different species, especially when the recent are compared with the older fossil species; moreover one of the chief characters between the genus Scalpellum and Pollicipes, depends on the direction of the lines of growth. In the scuta, terga, rostrum, and upper latera of the present species, the chief growth is downwards; in the carina, in mature specimens, it is both upwards and downwards; in the carinal latera, both upwards and towards the infra-median latera; in the infra-median latera chiefly upwards; and, lastly, in the rostral latera, towards the infra-median latera. Peduncle, short, not half as long as the capitulum; calcareous scales imbricated as usual, tinged red, almost crescent-shaped, acuminated at both ends, of remarkable length, so that in each whorl there are only four scales: a full-sized scale equals in length one of the rostral latera. The tips of two scales, in one whorl, lie under the middle points of the carina and rostrum; and in the whorl, both above and below, a single much curved scale occupies this same medial position. The peduncle does not seem to have been attached in any definite position to the horny coralline, as is the case with S. vulgare. Length of capitulum in the largest specimen .2 of an inch. The Mouth is directed towards the ventral surface of the thorax. The Labrum is far removed from the adductor muscle, with the upper part forming an overhanging projection; I believe there are some very minute bead-like teeth on the crest. Palpi, small, narrow, thinly clothed with bristles. Mandibles, with three teeth, of which the first is distant from the second; inferior angle not much acuminated, pectinated on both edges. Maxillæ, small, narrow, produced, without any notch, with two large upper spines, of which one is much thicker than the other; on the convex upper margin there are some minute tufts of very small hairs. Outer Maxillæ, with few bristles, arranged in a continuous line on the anterior surface; on the external surface there is a tuft of long bristles. Olfactory orifices situated laterally, forming two flattened, tubular projections. Cirri.--First pair placed not far from the second; the three posterior pair not very long, with their segments elongated, not protuberant, bearing four pair of non-serrated spines, with a single short bristle between each pair; dorsal tufts small, with one spine longer than the others. First cirrus rather short, segments not very broad; second cirrus with the rami nearly equal in length, anterior ramus rather thicker than the posterior ramus, with three longitudinal rows of spines. Caudal Appendages.--These are minute, rather broad, not half as long as the lower segments of the pedicels of the sixth cirrus, with four very long spines at the tip. Penis.--There is no trace of a probosciformed penis in the four specimens examined; and as this organ is present in every ordinary cirripede, with the exception of Ibla Cumingii which we know to be exclusively female, so we may infer with some confidence that the form here described is female, although it is impossible in specimens once dried to demonstrate the absence of the vesiculæ seminales and testes. Affinities.--This is a very distinct species; it is, however, much more nearly related to S. rutilum, than to any other species; and next to this, to S. vulgare; from this latter species it chiefly differs in the large scales of the peduncle, in the scuta not being added to at their upper ends, and in the membrane covering and connecting the valves being spineless; but there is a greater difference in the trophi and in the cirri. The peduncle of S. ornatum presents some resemblance to that of the singular cretaceous genus, Loricula. MALE. All the specimens, as already stated, were dry, but in an excellent state of preservation, so that after having been soaked in spirits, they could be minutely examined. In the four which I opened, I found, in a transverse pouch on the under side of each scutum, a male lodged; in a fifth dead and bleached specimen, the cavities in the shell for the reception of the males, were present; and in a sixth young specimen, also dead, cavities were in process of formation. As compared with plants, the relation of the sexes in this species may be briefly given, by saying that it belongs to the class Diandria monogynia. I will first describe the males themselves, and then the cavities in the shell of the female. The males differ in every point of detail, from the complemental males of S. vulgare, but yet present so close a general resemblance, that a comparative description will be most convenient. The general shape of the whole animal is rather more elongated, and I suspect flatter, but this latter point could not be positively ascertained in dry specimens. The entire length is greater, being in the largest specimen 13/400 (instead of at most 11/400), and the width, 7/400 of an inch. The orifice is not fimbriated; the four bristly points over the calcareous beads are absent. The whole outer integument is much thinner, owing evidently to its protected position, and is not covered by little bristles, but with an extremely high power, minute points arranged in transverse lines can be distinguished. The calcareous beads, or rudimentary valves, are thin and regularly oval. It is remarkable that in all the specimens, two on one side were smaller than the two on the other side,--the smaller beads being 16/6000, and the larger, 22/6000 of an inch in diameter; therefore more than twice the size of one of the beads in S. vulgare, which are only 9/6000 externally in diameter. From the position of the eye, close to one margin, near the upper end of the flattened animal, and from the manner in which the little limbs and spines lay between two of the beads at the opposite end, it was manifest that these latter, one large and one small, corresponded with the terga of the other cirripedes, and that the other two, near the eye, answered to the scuta. The valves being of unequal sizes on the right and left-hand sides of the animal, is probably connected with one side being pressed against the hard, shelly valve of the female; in the same way as the valves in certain Pæcilasmas; are smaller and flatter on the side nearest to the crustacean to which they are attached. The eye, in being slightly notched on the upper and lower edge, shows signs of really consisting of two eyes, which I believe is always normally the case; it is rather larger, in the proportion of 13 to 11, being 13/12,000 of an inch in diameter, than in S. vulgare; and from the almost perfect transparency of the integuments, is far more conspicuous than in that species. Hence when the valves of the female are opened, the black little eye is the first part of the male which catches the attention. No vestige of a mouth could be discovered. Thorax and Abdomen.--The thorax, as in S. vulgare, is highly extensible, and when stretched exhibits the same five transverse folds or articulations; when contracted, it is broader, so that even the truncated end of the abdomen is wider than the lower (properly anterior) end of the thorax in S. vulgare. Its thin outer integument is studded with excessively minute points in transverse rows. The four pair of limbs are longer than in S. vulgare, but the spines on them much shorter and thicker; each limb (including the first) supports three spines, of which one is seated on a notch low down on the outside, and is longer than the other two; of these two, the one on the same side with the notch, is a little longer than the other. The spines on the first and second pair of limbs are considerably shorter than those on the third pair, and these latter, are a little shorter than those on the fourth or posterior pair. Hence, the spines on the thoracic limbs, compared with those of S. vulgare, present considerable differences, both in their relative and absolute dimensions. The abdominal lobe is in proportion rather shorter; its end is less abruptly truncated, and supports a row of, I believe, six moderately long, and basally thick spines; these spines are not so long as those surmounting the fourth pair of limbs. On both lateral margins of the abdomen, rather on the ventral face, there is a row of, I believe, seven long spines, but it is very difficult to count the spines in specimens which have been once dried. I was able to distinguish that the two lower pair of spines on the ventral surface, are seated a little way one below and within the other, as in S. vulgare. The abdominal spines altogether form quite a brush, and there are certainly several more than in S. vulgare, and those on the two sides are much longer. Antennæ.--The disc is hoof-like, with the upper surface forming a straight line with the upper edge of the basal segment; the apex is pointed and clothed with some fine down; there is a single spine pointing backwards, which rises from the lower flat surface. The ultimate segment was hidden in laminæ of cement; and I was not able to make out its structure. There is a single spine on the outer edge of the basal segment, in the usual position. The entire length of the limb, measured from the end of the disc to the further margin of the basal articulation, is 36/6000ths of an inch; measured to the inner margin, it is; 21/6000ths of an inch; the disc itself is 12/6000ths of an inch long; these measurements differ a little both absolutely ad proportionally, compared with those of the antennæ of S. vulgare. Cavities in the Scuta of the Female for the reception of the Males.--These extend nearly parallel to the tergal margin, transversely across the valves, for three fourths of their width; they are seated above the depression for the adductor muscle, and are more conspicuous than it; they are deep and well defined, and each exactly contains one male. The males are placed with their orifices in a little notch in the occludent margin, and their prehensile antennæ at the further end. The distance to which the cavities extend across the valve, and their distance from the upper or tergal margin, varies a little, but chiefly in accordance with the age of the specimens; for the valve continues to increase in width, whilst the size of the cavity remains the same. The occludent margin of the scutum in the largest female, was .1 of an inch in length; of another, in which there was a fully developed cavity, .084; of a third, in which there was no cavity, only a slight concavity, with a preparatory impression, the length of the occludent margin was .062. The larger and smaller of these three valves, are drawn of their proper proportional sizes, in Pl. VI, figs. 1 b´, 1 c´. The preparatory impression (fig. 1 c´, b), consists of a narrow, not quite straight, extremely slight furrow, of slightly irregular width, bordered on each side by a very minute ridge, which is distinctly continuous with the inner edge of the occludent margin, both above and below the cavity. The furrow appears to have been formed by calcareous matter not having been deposited along this line, during the thickening or growth of the internal surface of the valve: I suspect, that it originates at a single period of growth, for I could see no signs of successively-formed transverse lines. I believe that it is strictly homologous with the fold, over which the complemental male is attached in S. vulgare, but carried, for a special purpose, much further across the valve and rectangularly inwards, for in structure and position both are identical. In comparing the internal views of the scuta in S. vulgare and S. ornatum (Pl. V, fig. 15 a´, and Pl. VI, fig. 1 c´), it must be borne in mind, that the latter should be compared, as clearly shown by the lines of growth, with that portion alone of the scutum in S. vulgare, which lies under the curved ridge connecting the umbo and tergo-lateral angle. The deep cavity in which the male is lodged, is formed subsequently to the preparatory furrow, simply by the gradual thickening of the surrounding surface of the valve, more especially of a ridge just above the pit for the adductor muscle, and of another broad ridge just beneath the tergal margin. The deepest part of the cavity lies parallel to the tergal margin along the upper side, and here, in the older valves, the preparatory furrow can by care be distinctly traced. In conformity with the shape of the cavity, the orifice or notch in the occludent margin of the scutum, is situated at the point where the preparatory furrow sweeps round and enters. I believe that the cavity is lined by membrane, and that between the cavity and the body of the female, there is a complex membranous layer,--a pouch or bag being thus formed. An imaginary section of this pouch (with the thickness of all the parts extremely exaggerated and in a reversed position) is given in Pl. VI, fig. 1 d´: a is the shell; x the cavity, converted, as I believe, into a pouch by, firstly, the delicate tunic (c) lining the sack of the female; secondly, a double layer (d) of corium; and, thirdly, by a special, rather thick membranous layer (b), which thinning out round the cavity coats only part of the under surface of the scutum. This latter membrane I have not seen in any other Cirripede, and I believe it is nothing but the tissue, here not calcified, which, in a calcified condition, ordinarily forms the valves. On this view, the males may be said to be lodged in pouches, formed in the thickness of the valves. Concluding Remarks.--The males from the absence of a mouth (and no doubt of a stomach), must necessarily be short-lived, and, I suppose, are periodically replaced by fresh males.[57] In one instance, the remnants of the two great compound eyes of the larva, could be seen at the end of the pouch, opposite the orifice. The larvæ, I conclude, crawl in at the orifice, one side of which is formed, as we have seen, of yielding membrane, and scratch out the dead exuviæ of the former occupant: certainly, the males are less firmly attached to their pouches, though some small quantity of cement is excreted, than are other Cirripedes to the objects to which they are attached. The small size of the female, and her valves not being thickly edged with chitine, accounts for the males having pouches specially formed for them, instead of being, as in S. vulgare, laterally imbedded in the chitine-border of the scuta. In hereafter weighing the evidence on the nature of the parasites in Ibla and in Scalpellum, the fact of the valves of the supposed female being here modified for the special purpose of lodging the males, will be seen to be important. If we imagine the male parasites to be extraneous animals, and that by adhering to the sack of the Scalpellum, they injure the corium and thus prevent the growth of the shell over an area exactly corresponding to their own size, and so form for themselves cavities; yet what can be said regarding the preparatory furrows? surely these narrow lines cannot have been produced by the pressure of the much broader parasites. Must we not see in the furrows, the first marking out, if such an expression may be used, of the habitation for the male, which has to be specially formed by the independent laws of growth of the female?

[57] It is possible, though opposed to all analogy, that the females may be short-lived, and breed only once, in which case the males would not have to be periodically replaced.

3. SCALPELLUM RUTILUM. Pl. VI, fig. 2. S. (Foem. an Herm.) valvis 14 sub-rufis: carinæ tecto plano, utrinque cristâ rotundatâ instructo; margine basali truncato: lateribus superioribus latitudine duplo longioribus. (Fem. or Herm.) Capitulum with 14 reddish valves: carina with the roof flat, bordered on each side by a rounded ridge; basal margin truncated: upper latera twice as long as broad. Mandibles with three teeth: maxillæ narrow, bearing only four or five pair of spines: segments of the second and third pair of cirri with one side wholly covered with spines. MALES, two, lodged in hollows, on the under sides of the scuta; pouch-formed, with four (?) rudimentary valves; no mouth; cirri not prehensile.

Hab. unknown; associated with Dichelaspis orthogonia. British Museum.

FEMALE OR HERMAPHRODITE. There is only a single specimen in the British Museum, and this had nearly all its valves separated, and many of them in fragments: from its state of decay, I think the specimen must have been dead, when originally collected. Description.--The capitulum consists of fourteen valves, including from analogy a rostrum.[58] Valves, apparently covered with membrane, bearing some thin spines on the margins; clouded with a fine, though pale, orange tint; surfaces plainly marked with lines of growth.

[58] In my first, and as I thought careful examination of the separated valves (my only materials) of this species, I mistook one of the triangular rostral latera for the rostrum, and hence was unfortunately led into an error in my 'Monograph on the Fossil Lepadidæ of Great Britain,' in which I state that the present species has only twelve valves in the capitulum; and I inferred from this, that S. quadratum, S. fossula, &c., had only twelve valves; I still believe this to be correct, but the existence of fourteen valves in S. rutilum and S. ornatum, the recent species to which the above fossils are most closely allied, no doubt is a strong argument in favour of this higher number.

Scuta, elongated, nearly three times as long as broad; apex, pointed; basal margin extremely oblique, forming an acute angle with the occludent margin; the lateral margin is slightly hollowed out, and is separated from the tergal margin by a large rectangular projection or shoulder. The occludent margin is nearly straight; externally, there is a slight ridge running down the middle of the valve, from the apex to the baso-lateral angle; and a second ridge running from the apex to the tergo-lateral angle. The lines of growth do not end abruptly at the tergo-lateral angle, as is the case with S. ornatum and several fossil species, but run up a little way along the tergal margin. The umbo is seated at the uppermost point, and, therefore, the main growth is downwards. There is a large rounded depression for the adductor muscle (a, fig. 2 a´), and higher up, opposite the tergo-lateral angle, there is another hollow (b), for the lodgment of the males; this latter is of nearly the same shape as the hollow for the adductor muscle, but rather more conspicuous than it. From the appearance of the under surface of the scuta, it might readily have been thought, that there had been two adductor muscles. Terga, of large size, longer than the scuta, flat, triangular, with the whole inferior part much produced and spear-like. A portion of the apex, must have projected freely above the sack. Carina (Pl. VI, fig. 2 b´), simply bowed (i. e., not rectangularly bent), with the umbo (and primordial valve) seated at the upper point; rather massive, narrow, only slightly increasing in width from the upper to the lower end; the two sides are flat, and at right angles to the roof, which is bordered on each side by a rather broad, square-topped ridge (see section fig. 2 c´), or the roof may be said to have a square-edged furrow running from the apex to the basal margin, and widening downwards; these two ridges have their lines of growth oblique, and hence have a twisted appearance; the central depressed portion of the basal margin, which is square or truncated, descends lower down than the two ridges. The sides of the valve close to the apex are broad, and consist, as I believe, of intra-parietes, as well as of parietes, but these parts are not separated from each other by ridges, as is commonly the case, more especially with the fossil species. I have described the carina in some detail, on account of its resemblance to that of the cretaceous S. fossula, S. trilineatum, and S. quadricarinatum. Rostrum, unknown; but one probably existed. Upper Latera, of large size, elongated, quadrilateral, approaching to diamond-shaped, with the angles rounded, nearly twice as long as broad; almost flat; upper half acuminated, lying between the scuta and terga; the lower half broad, forming a rectangular projection lying between two latera of the lower whorl. The umbo is near the apex, the greater part of the growth being downwards, but the valve is added to a little, round the two sides of the apex; these additions do not take place in the early stages of growth, (as explained under S. vulgare,) and, therefore, they form a depressed rim. Rostral Latera, almost exactly triangular, curved; basal margin furnished with a just perceptible rim. Infra-median Latera, quadrilateral, sides unequal in length; the carino-basal margin being the longest; in area not quite twice double the rostral latera; directed obliquely upwards. Carinal Latera, sub-triangular, produced upwards, with the apex rounded, and the two lateral margins hollowed out; the basal margin exceeds a little in length the basal margin of the rostral latera. The umbones of these two latera are seated at their basal outer angles, so that the growth of the valves is towards each other and upwards. The umbo of the infra-median latus is seated at the baso-rostral angle, and hence the growth is obliquely upwards. The umbones of the rostral latera must have been close together, over the unknown rostrum. Length of capitulum about 4/10th of an inch. Peduncle, only small fragments are preserved; the calcified scales are small, closely imbricated, several of them together only equalling in length the basal margin of the rostral latera. Each scale is thin, transversely elongated; basal imbedded portion straight; upper margin rounded. Mouth.--Labrum with the upper part highly bullate, forming an overhanging projection; palpi apparently small and narrow. Mandibles, narrow, produced, with three teeth; inferior angle pectinated, as is sometimes the third tooth; the distance between the tips of the first and second teeth equals that between the second tooth and the inferior angle. Maxillæ, extremely narrow, produced, without any notch; spinose edge exactly one third of the length of the mandibles: beneath the two upper great spines there are only three or four pair of spines; on the convex upper margin there are some minute tufts of the smallest hairs. Outer Maxillæ, rounded with the inner margins very sparingly but continuously covered with bristles. I could not ascertain whether the olfactory orifices were tubular. Cirri.--These consisted, in the one specimen, of merely small fragments. The segments of the posterior cirri are elongated, not protuberant, and support, I believe, five pair of non-serrated spines, and an exterior row of very minute spines: dorsal spines fine and long. Either the second or third cirri, or probably both, are remarkable for having the whole of one side of each segment covered with irregular rows of long spines. Moreover, in the upper segments of these same cirri, between each separate dorsal tuft, there is placed one or two long bristles. The first cirrus appears to have had very broad segments, and these are singular from the spines in the dorsal rows, being extremely long. In some of the cirri, several of the basal segments are soldered together. Caudal Appendages, lost. From the state of the specimen, it was quite impossible to ascertain whether the individual here described was an hermaphrodite or female; from the analogy of its nearest congener, S. ornatum, the latter is the most probable; but the genus Ibla shows how the sexes may differ in the most closely-allied forms. Affinities.--From the hollows on the under sides of the scuta, for the lodgment of the males; from the umbones of the scuta and of the carina being situated on the apices of these valves; and from all the characters of the mouth, S. rutilum is much more closely allied to S. ornatum than to any other species. MALE, OR COMPLEMENTAL MALE. In the concavity or hollow above the depression for the adductor muscle (Pl. VI, fig. 2 a´), I found males, but in so extremely decayed a condition, that they could hardly be examined. On one side, however, I distinctly saw the larval prehensile antennæ, with pointed, hoof-like discs; and part of the thorax, with its small limbs and long spines, as in S. vulgare or S. ornatum. I also saw clearly the eye. The four calcified beads or rudimentary valves, I believe, were present; but in removing the specimen, the whole fell to pieces and was lost. The outer integument was covered with rather thick, very minute bristles, each about, 2/10,000th of an inch in length, and therefore only half the length of those on the complemental males of S. vulgare. The cavities for the males are not formed, as in S. ornatum, by the thickening of the internal surface of the valve round a defined space, but by the scutum being externally convex and internally concave down the middle, hollows being thus produced both for the lodgment of the males and for the attachment of the adductor muscle. These hollows are separated from each other by a slight transverse ridge. I do not know at which point of the margin of the valve, the orifice of the male is situated, but I presume close under the apex. In this species, as in S. ornatum, there can be no question that the scuta of the female are specially modified by their own growth for the reception of the males. It must be added that, as it was not possible to ascertain whether the ordinary form of S. rutilum was hermaphrodite or female, so it must remain doubtful whether the parasites are males or complemental males; but the former, I think, is most probable. [=TT= SUB-CARINÂ PRESENTE.] 4. SCALPELLUM ROSTRATUM. Pl. VI, fig. 7. S. (Herm.) valvis 15: rostro permagno: laterum paribus quatuor: pari superiore pentagono. (Herm.) Capitulum with 15 valves: rostrum very large: four pair of latera; upper latera pentagonal. Mandibles with four teeth; maxillæ with the inferior angle prominent. Complemental Male, attached between the mouth and adductor scutorum muscle; pedunculated; capitulum bearing a pair of elongated scuta and a rudimentary carina; mouth and cirri prehensile.

Philippine Archipelago; Island of Bantayan. Attached to a horny coralline: 20 fathoms. Mus. Cuming.

HERMAPHRODITE. Capitulum, with the upper part narrow and produced. Valves, 15 in number, placed close together, clouded pale red, covered with membrane, which is thickly clothed with minute points. Scuta rather small, oval, with the upper end pointed; rather convex; basal and lateral margins blending into each other; the upper produced portion above the umbo is small; there is a deep pit for the adductor muscle, and there is a fold on the occludent margin in the usual position; occludent margin not straight. Terga large, one third of their own length longer than the scuta; fat, sub-triangular; the three margins are not quite straight; the carinal margin projects a little above the apex of the carina, and the scutal margin is excised to fit the upper part of the scuta. Carina bowed, internally deeply concave; upper portion above the umbo, about one fourth of the total length, extending between the terga for two thirds of their length, up to the slight prominences on their carinal margins: a ridge separates, on each side, the parietes from the tectum. Rostrum (fig. 7 a) unusually large, about two thirds of the length of the scuta, and twice as long as the rostral pair of latera; internally concave, externally carinated; outline of the upper portion acutely triangular, of the lower portion rounded; umbo seated at the upper end. Upper Latera pentagonal, with the apex rounded. Rostral Latera flat, four-sided, with the basal margin the longest, and the baso-carinal angle produced. Infra-median Latera nearly equalling in area the upper latera; not descending so low down as the rostral and carinal latera; outline of lower half semi-oval, of upper half rectangular. Carinal Latera flat, four-sided, with the basal margin the longest, and slightly protuberant; baso-rostral angle produced; whole valve larger than the rostral latus, but closely resembling it in form. Sub-carina minute, not above one third of the size of the rostral latera, which are the smallest of the other valves; internally deeply concave; externally solid, pyramidal, standing out beyond the surface of the carina, with the umbo at the apex. The umbones of the four pair of latera are seated a little above the centre in each valve, on the summit of a raised triangular portion; this arises from the valve at first growing only downwards, and when added to at the upper end, the new part forms a ledge at a lower level round the old part, which had already acquired some thickness. Peduncle, short, about half the length of the capitulum; narrow; thickly clothed with minute, longitudinally elongated, spindle-shaped, calcareous scales or beads, which project but little. Length of the capitulum, rather under 3/10ths of an inch. In a Young Specimen, with its capitulum, together with the peduncle, only 1/10th of an inch long, the scuta, terga, and carina are very large in proportion to the valves of the lower whorl. The latter project more, and are externally more pointed, as in the genus Pollicipes. The rostrum is well developed; the infra-median latera, in proportion, are the least of all the valves. The carina is straight and pointed, and not, relatively to the scuta, quite so long. The scuta are rather broader in proportion to their length, which would naturally follow from less having been added to their apices,--these valves at first growing only downwards. The membrane covering and connecting the valves is furnished with long thin spines. Mouth.--Labrum placed far from the adductor scutorum muscle, with the upper part exceedingly prominent; apparently there are no teeth on the crest. Palpi blunt. Mandibles, narrow, with four teeth, of which the second is not smaller than the others; inferior angle sharp and produced, barely pectinated. Maxillæ.--Under the two or three great upper spines, there is a tuft of fine bristles; the inferior part of the edge is step-like, and much upraised. Outer Maxillæ, with the inner edge deeply notched, and the bristles arranged in two quite distinct tufts; the bristles on the outer surface are long. Olfactory orifices, thin, tubular, and projecting. Cirri.--The first pair is placed far from the second; the three posterior pair are long and straight, with their segments much elongated, not protuberant, bearing four or five pair of long spines, with little intermediate tufts of minute spines, and with the minutest spines on the lateral upper edges. Dorsal tufts with one spine extremely long, equalling a segment and a half in length; the others very short. Spines all serrated. First cirrus not very short; rami nearly equal, with the four terminal segments of both tapering; all the basal segments much thicker, and thickly covered with bristles. Second cirrus (as well as the third in a less degree), with the anterior ramus thicker than the posterior ramus, and with all the lower segments in both rami thickly clothed with three or four longitudinal rows of spines. Caudal Appendages, spinose, uni-articulate; but the specimen was injured, and I could not exactly make out their shape: I believe it was oval, and thickly fringed with fine spines. Penis, very small, almost rudimentary, narrow, and hairy, scarcely exceeding in length the pedicel of the sixth cirrus. COMPLEMENTAL MALE. Pl. VI, fig. 5. Before describing the parasite of the present species, which departs entirely from the character of the males of the three preceding species, it is proper to state that I consider it to be a Complemental Male simply from analogy, as will hereafter be more fully shown at the end of the genus. Had a specimen of the parasite been brought to me without any information, I should have concluded that it was an immature individual of a new genus of pedunculated Cirripedes, remarkable from the rudimentary condition of the valves, and exhibiting, in one important character, namely, in the form of the larval prehensile antennæ, an alliance to Scalpellum. Had I been then told that three individuals in a group, had been found attached to S. rostratum, not outside the valves, but to the integument, in a central line, between the labrum and the adductor scutorum muscle, in such a position that when the Scalpellum closed its valves, these parasites were enclosed within the capitulum, my surprise would have been great; for it is very improbable that this singular and unparalleled position was accidental in this one group of specimens, inasmuch as there seems to be a relation between the naked condition of the capitulum of the parasite, and the protection afforded to it by the capitulum of the Scalpellum. It further becomes apparent on reflection, that these minute parasites, though having the appearance of immaturity, can not increase in size, or but little, for if they did grow, and acquired an ordinary size, they would either be killed by the pressure of the scuta of the Scalpellum, or they would destroy the latter, and in doing so soon lose their own support, and thus necessarily perish! The one full-grown specimen of S. rostratum, in Mr. Cuming's collection, was in a good state of preservation, but dry. The three parasites were attached, as stated, close under the labrum, between it and the adductor muscle. They are constructed like ordinary Cirripedia, and have a mouth, thorax and cirri, enclosed in a capitulum, supported on a peduncle of moderate length and narrow. The entire length of the capitulum and peduncle, as far as could be ascertained in the shrivelled condition of the specimens, was 35/1000ths, and the greatest width of the capitulum 11/1000ths of an inch. Both capitulum and peduncle are hirsute with spines, nearly 1/1000th of an inch in length, mingled with shorter hairs in little rows of three and four together. The figure (5) in Pl. VI is merely a restoration, as accurate as could be made from the much shrivelled specimens. There are only three valves,--namely, an oval carina (a), seated rather high up on the capitulum, in a rudimentary condition and only 1/1000th of an inch in length, and a pair of scuta; these latter consist of a narrow, slightly curved plate, 8/1000ths in length, broadest at the lower end, where the breadth is 2/1000ths of an inch. The prehensile antennæ, at the end of the peduncle, have pointed hoof-like discs: I was not able to make out the other parts. It deserves notice, that in the young specimen of the ordinary form of S. rostratum, 1/10th of an inch in length, and therefore only thrice as long as the parasites, all the valves were perfect, and seemed to have followed the ordinary law of development. Mouth.--The largely bullate labrum is placed far from the adductor, in the same manner as in the hermaphrodite. The mandibles have three large sharp teeth, with the inferior point very sharp and small, so that there is one less tooth than in the hermaphrodite. The maxillæ have two or three large upper spines, the others being very thin; I believe the lower part is upraised and step-like, as in the hermaphrodite. The outer maxillæ are bilobed in front, with a few short bristles on the outer side near the bottom. I was not able, from the dried state of the specimens, to discover whether the olfactory orifices were tubular. Altogether it was apparent, from this imperfect examination, that there was a close similarity between the mouth of the parasite and of the hermaphrodite. The Thorax is unusually elongated. Cirri.--The first pair is very short, and is distant from the second. All have the appearance of immaturity, with their pedicels very long in proportion to their rami; the latter are slightly unequal in length, even in the sixth pair. There appeared to be six segments in the rami of the sixth pair, each segment bearing two or three pair of long spines. Caudal Appendages, with two or three little spines on their summits. Penis, short, blunt, thick at the apex, with one or two spines on it. I did not see any ovaria, but this could hardly have been expected in specimens in a dried condition, without they had happened to have been in a gorged condition. Certainly there were no ova. In the general summary at the end of the genus, I shall give my reasons for believing this parasite to be the Complemental Male of the Scalpellum rostratum. 5. SCALPELLUM PERONII. Pl. VI, fig. 6.

SMILIUM PERONII. J. E. Gray. Annals of Philosoph., new series, tom. x, 1825. ---- ---- . . . . . Spicilegia Zoologica, tab. iii, fig. 10, 1830. ANATIFA OBLIQUA. Quoy et Gaimard. Voyage de l'Astrolabe, Pl. xciii, fig. 16, 1823-1834. POLLICIPES OBLIQUA. Lamarck. An. sans Vertebres (2d edition).

S. (Herm.) valvis 13: laterum paribus tribus; pari superiore multùm elongato: pedunculi squamis calcareis nullis. (Herm.) Capitulum with 13 valves: three pair of latera; upper latera much elongated: peduncle without calcareous scales. Mandibles with 10 or 11 unequal teeth: maxillæ with the edge nearly straight, bearing numerous spines. COMPLEMENTAL MALE, attached externally, between the scuta and below the adductor muscle; pedunculated; capitulum formed of six valves, with the carina descending far beneath the basal angle of the terga; mouth and cirri prehensile.

Swan River, Australia, attached to a coralline; Mus. Cuming. Port Western, Bass's Straits, as stated in the Voyage of the Astrolabe. Mus. Brit.

HERMAPHRODITE. Capitulum formed of 13 valves; namely, two scuta, two terga, a carina and sub-carina, a rostrum, a pair of upper latera, and two pair of lower latera; these latter valves, with the sub-carina and the rostrum, make a whorl of six pieces. The upper part of the capitulum is, as usual, produced. The upper valves are separated (in specimens which have not been dried) by rather wide interspaces of membrane; they are covered (excepting, generally, their umbones,) by membrane, which in the interspaces is clothed with fine spines. The spines, or the marks where they were once articulated, are visible over nearly the entire surface of the membrane covering the valves. The spines are particularly numerous round the orifice of the sack. The whole capitulum, (in a dried condition), is coloured dull purplish-red, which is only in part due to the underlying corium, for the valves themselves are pale red. After having been long kept in spirits, the whole capitulum becomes colourless. The valves are smooth, faintly marked by lines of growth. The umbones of the lower valves project outwards, giving a denticulated appearance to the base of the capitulum. Scuta, slightly convex, oblong, breadth about two thirds of the length, almost quadrilateral, with the upper portion produced into a flat projection; this projection is almost spear-shaped, being constricted a little on each side below the apex. There is a deep pit for the adductor muscle. The umbo is near the apex, the part above not being above one fifth of the whole length of the valve. As in S. vulgare, the growth is at first downwards, and subsequently a little upwards and downwards, thus producing the upper, small, spear-like projection, which lies at a lower level than the umbo. There is a fold on the occludent margin. Terga, large, flat, triangular; carinal margin slightly hollowed out; occludent margin slightly arched, with a small portion protuberant to a variable amount. The apex is slightly curved towards the carina. Carina, long, internally deeply concave, angularly bent, the lower portion slightly longer and wider than the upper part; the two halves meet each other at about an angle of 135°; the upper half is parallel to the longer axis of the terga, between which it extends for three fourths of their length. The external surface is rounded, except near the umbo, where the edge is carinated; growth almost equally upwards and downwards; the parietes and tectum are not separated by ridges. The Sub-carina lies close under the carina, and is placed almost transversely to the longer axis of the capitulum; external surface arched and smooth, the whole having the shape of half of a cone, with the apex a little curved outwards; seen internally, it may be said to be formed of two triangular wings placed at right angles to each other; basal margin straight; in size equalling the carinal latera. Rostrum, lying almost transversely to the longer axis of the capitulum, under the basal margins of the scuta; in shape (fig. 6 a) closely resembling the sub-carina, but about one third larger than it; larger also than either the rostral or carinal latera; seen externally, appears like a half cone; seen internally, is formed of two triangular wings (with curved edges), placed at right-angles to each other. Upper Latera, internally flat, oblong, twice as long as broad; upper end square, truncated; upper half rather wider than the lower half; fully twice as large as either of the lower latera. The basal points extend below the basal margins of the scuta. The umbo is placed a little above the centre. Rostral Latera, minute, scarcely exceeding one third of the size of the carinal latera, and very much less than the rostrum; they are placed transversely under the basal point of the upper latus, or rather between it and the baso-lateral angle of the scutum; basal margin, as seen internally, straight; upper margin arched; rostral angle produced; internally flat; the whole valve is very thick and solid, so that the umbo which lies at the rostral end, projects rectangularly outwards. Carinal Latera, oblong, nearly quadrilateral, with the upper angle produced; placed obliquely, parallel to the lower half of the upper latera; umbo slightly prominent, seated near the apex, with three rounded ridges proceeding from it; internal surface very slightly concave. Peduncle and Attachment.--The peduncle is short, not equalling the capitulum in length. The whole surface is most thickly clothed with minute spines, which are not visible when the specimen is dry; I think it probable that they may sometimes all drop off before a new period of exuviation. The peduncle does not (at least in the specimens which I have examined, which were grouped in a bunch) taper at the lower end to a point; and after careful examination, I feel sure that the cement does not debouch from several successively formed orifices, as in S. vulgare and as in some Pollicipes, but only from the two original orifices in the prehensile antennæ of the larva. In these latter organs, the sucking disc is hoof-like and pointed, and is narrower than the basal segment. The ultimate segment has on its inner side (supposing this segment stretched straight forwards,) a notch or step bearing at least three spines. The proportions of the different parts differ slightly from those in S. vulgare; but, as I shall hereafter have to give all the measurements, I do not think them worth repeating here. In the one large group of specimens examined by me, in Mr. Cuming's possession, all were attached symmetrically to the coralline, as in the case of S. vulgare, capitulum upwards, and their carinas outwards. Length of capitulum about three quarters of an inch; width about half an inch; entire length, with peduncle, a little more than one inch. The Mouth is placed far from the adductor muscle. Labrum, with its basal margin much produced; upper part highly bullate, forming a rounded projection equalling the longitudinal axis of the rest of the mouth; crest without any teeth. Palpi, triangular, with the two margins, thickly clothed with bristles; on each side of the mouth, near where the palpi are united to the mandibles, there is a slight, orbicular, shield-like swelling. The Mandibles (Pl. X, fig. 3) have nine or ten very unequal teeth, with the inferior angle rather broad and pectinated; of these, there are four main teeth, of which the second is always the smallest, and between the four, one or two small teeth are interpolated; so that the total number is either nine or ten, and often varies on the two sides of the same individual, as likewise does the shape of the inferior angle. Maxillæ, with the edge nearly half as long as that of the mandibles, supporting from seventeen to twenty pairs of spines; the upper pair is only slightly larger than the others; a part near the inferior angle projects slightly beyond the rest of the nearly straight edge. The apodeme, at its base or point of origin, is unusually broad and flat. Outer Maxillæ, large and triangular. The inner margin is slightly concave, and continuously covered with short spines. The outer margin is bilobed, as in S. vulgare, with the basal part supporting a great tuft of long bristles, of which the greater number turn outwards, and almost cover the olfactory orifices. The latter are slightly prominent, placed some way apart from each other, with the above-mentioned tufts of bristles between them. All the spines of the trophi are in some degree doubly serrated. Cirri.--The first pair is seated rather far from the second pair, and the prosoma being little developed, the shape of the body nearly resembles that of S. vulgare. The posterior cirri are elongated, very little curled, with the segments much flattened, not at all protuberant, bearing from five to seven pair of long serrated spines, with a few small spines in an exterior row; between each pair there is a very minute tuft of small bristles; the upper lateral rim of each segment is toothed with small spines; spines of the dorsal tufts, long, serrated. First pair, elongated, having numerous segments, namely, seventeen, whilst the sixth pair in the same individual had only twenty-one segments; rami nearly equal; segments short, nearly cylindrical, thickly clothed with long serrated spines. The second and third pair are nearly equal in length; they have their anterior rami slightly thicker than their posterior rami, both being much more thickly clothed with spines, than are the three posterior pair of cirri. Pedicels, rather short, with their inner edges not forming a projection, as in S. vulgare. Caudal Appendages (Pl. X, fig. 20), uni-articulate, flat, rounded at their ends and moderately long; clothed most thickly, like brushes, with very fine bristles, which latter are serrated, and are longer than the appendages themselves. Penis, of small size, narrow, pointed, and thickly clothed with delicate hairs; in length equalling only one fourth of the sixth cirrus. Ovigerous Fræna, small, semicircular; entire edge thickly covered with glands. Ovarian tubes, within the peduncle, fully developed as usual. Affinities.--This species differs from all the others in the absence of calcareous scales on the peduncle; but it has no other character which at all justifies its generic separation. In the shape of the scuta and carina it comes nearest to S. vulgare. Taking all the characters together, it is scarcely possible to say to which of the other species it is most closely allied, having close affinities with all. In the entire structure, however, of the Complemental Male, immediately to be described, this species certainly comes nearer to S. villosum than to any other species. I may add, that in S. villosum the latera are almost rudimentary, and therefore tend to disappear, whereas in S. Peronii it is the calcareous scales on the peduncle which have actually disappeared. COMPLEMENTAL MALE. Pl. VI, fig. 3. I examined, owing to the great kindness of Mr. Cunning, six dry specimens of the hermaphrodite S. Peronii, from Swan River, and one in spirits from another locality, in the British Museum. Out of these seven specimens, only three appeared to have had parasites attached to them, and these I infer, from reasons to be more fully given at the end of the genus, are Complemental Males. One of the three specimens, however, had two males close together. These parasites were firmly cemented to the integument of the hermaphrodite, in a fold, in a central line between the scuta, a little below (the animal being in the position in which it is figured) the adductor scutorum muscle, and therefore some way below the umbones of these valves. When the scuta are closed, the parasites, from their small size, are enclosed and protected. In every detail of structure, they are obviously pedunculated Cirripedia. The Capitulum (Pl. VI, fig. 3) has six valves; namely, a pair of scuta and of terga, a carina, and a rostrum, all united by finely-villose membrane, furnished near the orifice with some much longer and thicker spines. The capitulum is truncated in a remarkable manner, the orifice not being, as in the hermaphrodite, in the same line with the peduncle, but almost transverse to it, and therefore almost parallel to the surface of attachment. The largest specimen measured transversely, through the scuta and terga, was 30/1000ths of an inch in breadth; another was only 26/1000ths to 27/1000ths: this latter specimen, measured longitudinally, from the base of the carina to the tips of the terga, was 15/1000ths of an inch. A scutum of the largest specimen was 17/1000ths in length. The scuta and terga are broadly oval, with the primordial valves very plain at their upper ends. I may here mention, that in a central line between the scuta, I observed the apparently single, minute, black eye, as in ordinary Cirripedia. The Carina is straight, triangular, and internally slightly concave; its basal margin descends far below the basal points of the terga. The Rostrum is shorter, and internally more concave than the carina: I believe it projects more abruptly outwards than is represented in the figure. The Peduncle commences some little way below the scuta: it is narrow and very short: it is finely villose: it is lined by delicate transverse striæ-less muscles, within which there are the usual stronger, longitudinal muscles. The base is flat and truncated. I examined, and carefully compared, the prehensile antennæ with those of the hermaphrodite, and found every part and every measurement the same. The full importance of this identity will hereafter be more fully insisted on. The antennæ are represented of their proper proportional size in fig. 3. Mouth.--The labrum, as in the hermaphrodite, is highly bullate, and far removed from the adductor scutorum muscle. The Palpi are small and triangular, with their blunt apices clothed with a very few scattered bristles. Mandibles, with only three teeth, and the lower angle minute, slightly pectinated; the first tooth is distant from the second, and larger than it. Width of the whole organ, .0021 of an inch. Maxillæ, bearing only a few spines, furnished with a long apodeme; beneath the upper large pair there is a notch, under which there are two spines of considerable size and a small tuft of fine bristles; width .001 of an inch, and therefore only 1/16th of the size of the same organ in the hermaphrodite: the relative sizes of the maxillæ and mandibles are the same in the male and hermaphrodite. Outer Maxillæ blunt, triangular, with a few thinly-scattered bristles on the inner face; those on the outside being longer. Cirri.--The First pair is far removed from the second; the rami are very short, barely exceeding the pedicel in length; they are formed of only four segments, each bearing a pair of spines; but on the end of the terminal segment, there are three spines, of which the central one is very long. Second pair also short. In the sixth pair there are five or six elongated segments, each bearing three pair of long spines; dorsal tufts large. The cirri are furnished with transversely-striated muscles. The Caudal Appendages exist as two very minute plates, with a few bristles at their apices. The Penis is not acuminated, with four bristles at the end; it is short, equalling only the lower segment of the pedicel of the sixth cirrus. In the one specimen preserved in spirits, I unfortunately omitted to search for the vesiculæ seminales; I cannot doubt that such existed, but it would have been important to have ascertained whether they contained spermatozoa. I made out, most distinctly, that there was no trace of ovarian tubes within the peduncle; and my assertion may be believed when I state, that I traced the two much finer and more transparent cement-ducts, from the prehensile antennæ up to the body of the animal: in Lepas I have repeatedly detected, with ease, the ovarian tubes within the peduncle, before the calcification of the valves had even commenced, and therefore at a much earlier period of growth than in these parasites. Consequently I am prepared to affirm, that these parasites are not females, but that, as far as can be judged, from external organs, they are exclusively males. Concluding Remarks.--In comparing the capitulum of the hermaphrodite with that of the complemental male (Pl. VI, figs. 6 and 3), we must be struck with the differences in their shape, in the number, relative sizes, and forms of the several valves. It should, however, be borne in mind, that the scuta and carina in the hermaphrodite at first grow exclusively downwards; so that if we remove the upper portions subsequently added, the difference in shape in these valves is not so great as it at first appears. The rostrum in the male is of much larger relative size; whilst of the upper latera there is not a trace, although in the hermaphrodite these valves are larger than the rostrum. The terga, compared with those of the hermaphrodite, differ more essentially than do the other valves; and the manner in which the primordial valves project, shows that from the first commencement of calcification, the lines of growth have followed an unusual course. The great breadth and shortness of the terga is evidently related to the shortening of the whole capitulum, and the transverse position of the orifice; and this shortening of the capitulum, no doubt, is rendered necessary for its reception and protection within the shallow furrow between the scuta of the hermaphrodite. Finally, if we compare the internal parts of the hermaphrodite and male, the differences are considerable, though partly to be accounted for by the youth of the latter: the form and position of the labrum, and the distance between the first and second pair of cirri, is the same in both; but the mandibles and maxillæ differ considerably. To put the case as I have before done, if a specimen of one of these parasites had been brought to me to class without any information of its habits,--the downward direction of growth in all the valves, the presence of a rostrum, the villose outer integument, all the details of the prehensile antennæ, the form of the animal's body, and the position of the labrum, would have convinced me that, though a quite new genus, it ought to have stood close to Scalpellum, and nearer to it than to Ibla. 6. SCALPELLUM VILLOSUM. Pl. VI, fig. 8.

POLLICIPES VILLOSUS on Plate (TOMENTOSUS in text). Leach. Encyclop. Brit., Suppl., vol. iii, 1824, Pl. lvii. ---- VILLOSUS.[59] G. B. Sowerby. Genera of Shells, Pollicipes, fig. 3, 1826. CALANTICA HOMII. J. E. Gray. Annals of Phil., vol. x, p. 100, 1825. [59] As Mr. Sowerby has adopted the name villosus, I have followed him; though as tomentosus is used through some mistake by Leach in the text, both names have equal claims as far as priority is concerned. In Lamarck, 'Animaux Sans. Vert.,' the P. villosus of Sowerby is made synonymous with Anatifa villosa of Brugière, which is certainly incorrect, although the A. villosa of this latter author is not positively known.

S. (Herm.) valvis 14: sub-rostro præsente: carinâ pæne rectâ: laterum paribus tribus; pari superiore triangulo. (Herm.) Capitulum with 14 valves: sub-rostrum present: carina nearly straight: three pair of latera; upper latera triangular. Mandibles with four teeth, of which the second is the smallest: maxillæ with a projection near the inferior angle: no caudal appendage. COMPLEMENTAL MALE, attached externally between the scuta, below the adductor muscle; pedunculated; capitulum formed of six valves, with the carina not descending much below the basal angles of the terga: mouth and cirri prehensile.

Eastern Seas[60] (?) attached to shells and rocks. Mus. Brit.; College of Surgeons; Cuming. [60] No habitat is attached to any of these specimens; but Mr. Sowerby informs me that he has seen specimens attached to the Modiola albicostata of Lamarck, which shell is said by the latter author to be found in the seas of India, Timor, and New Holland.

HERMAPHRODITE. Capitulum with fourteen valves, consisting of a pair of scuta and of terga, a carina, (which five valves are much larger than the others,) a rostrum, sub-rostrum, sub-carina, and three pair of small latera. All the valves are covered by membrane, as are the calcareous scales on the peduncle; and this membrane everywhere is densely clothed with spines. The upper valves are not very thick; they stand rather close together. The eight valves of the lower whorl are more solid, and are placed far apart; they are small, tending to become rudimentary. None of the valves are added to at their upper ends, in which respect this species differs remarkably from the others of the genus, and approaches in character to Pollicipes. Scuta, with a deep hollow for the adductor muscle, triangular, with the basal margin elongated, and protuberant. Terga, large, flat, triangular, basal point blunt, with the carinal margin slightly hollowed out, and the scutal margin protuberant. Apex solid. Carina, rather longer than the terga, straight, gradually widening from the upper to the basal end, deeply concave. In young specimens the upper part is slightly bowed inwards. Apex solid. Sub-carina, with the inner surface crescent-shaped; the umbo points transversely outwards; in width it exceeds the largest of the latera. Rostrum, triangular, internally (fig. 8 a) concave; basal margin slightly hollowed out, and deeply notched; rather less in width than the carina; short, with the umbo pointing upwards and outwards. In young specimens the apex curves a little inwards. Sub-rostrum, with the inner surface transversely elongated (fig. 8 b), slightly crescent-shaped, about two thirds as wide as the rostrum. The apex points transversely outwards. Latera, three pair; the middle pair apparently corresponds with the upper latera of the other species of the genus. The two other pair of latera, together with the rostrum and sub-carina, form a whorl. The sub-rostrum lies by itself, a little beneath this whorl. The latera are smaller than the rostrum or the sub-carina. They are placed far distant from each other; their inner surfaces are triangular; their umbones point upwards; the rostral pair is smaller than the other two pair, which are of equal size. The exact position of the rostral latus differed on the two sides of the specimen examined; apparently its normal position is at the baso-lateral angle of the scuta. Peduncle, wide at the summit, longer than the capitulum; calcified scales small, not arranged very regularly; flattened, spindle-shaped, rather far separated from each other; imbedded in membrane, so that even their summits are rarely uncovered. The surface of the membrane is thickly clothed with spines, which are strong, thick, yellow, pointed, and furnished with large tubuli running to the underlying corium. These spines are arranged in groups of from three or four, to five or six. Besides these larger spines, the whole surface is villose with very minute colourless spines, not above 1/20th of the length of the larger ones. The surface of attachment is broad. This species, not being symmetrically attached to a coralline, the peduncle does not curve, as in most of the other species, towards the rostrum. The capitulum is above half an inch in length. Mouth.--The labrum is much produced downwards, but yet the mouth is not very far distant from the adductor muscle: the upper part is bullate, forming a small overhanging point, and in longitudinal diameter equals the rest of the mouth. Palpi blunt. Mandibles with four teeth, strong, short, thick, the second tooth much smaller than the others; inferior angle broad, pectinated. Maxillæ with a long, rather sinuous edge, which, near the inferior angle, has a narrow projecting point, bearing rather finer spines; there is, also, apparently, a very minute tuft of small spines close under the two large upper spines: there are, altogether, about twenty pair of spines, without counting the smaller ones. Outer Maxillæ, with the inner edge slightly concave, continuously covered with bristles; exteriorly, with a prominence covered with longer bristles. Olfactory orifices prominent, protected by a slight punctured swelling between the bases of the first pair of cirri. Cirri.--Prosoma moderately developed; first pair of cirri rather far removed from the second pair. The segments of the three posterior pair are not elongated, short, slightly protuberant in front, bearing four or five pairs of strong spines; a little below each pair, there is an intermediate tuft of very fine straight bristles, of which the upper tuft is the largest; on the lateral upper rims there are some short, strong spines; dorsal tufts rather small and thick; spines all more or less serrated, especially on the broad basal segments of the three anterior cirri. Pedicels of the cirri not particularly protuberant in front. First cirrus with rami, slightly unequal in length; not short; basal segments much thicker and more protuberant than the upper segments. Second cirrus; anterior ramus with six or seven basal segments highly protuberant, and crowded with spines; posterior ramus with about six segments, similarly characterised. Third cirrus with the anterior ramus having six, and the posterior ramus five segments, also similarly characterised. Caudal Appendages absent, there being only a slight swelling on each side of the anus. The oesophagus runs parallel to the labrum, and enters obliquely the summit of the stomach, which is destitute of cæca: the biliary envelope is longitudinally plicated. There are no Filamentary Appendages. Testes large, branched like a stag's horns, attached in a sheet to the ventral surface of the stomach: the vesiculæ seminales enter the prosoma, and have their reflexed ends not very blunt. The Penis is rather narrow, with the terminal half plainly ringed, and bearing tufts of fine bristles arranged in circles, one tuft below the other; on the basal half there are only a few scattered minute bristles. Affinities.--In the downward growth of all the valves, in the presence of a sub-rostrum, in the shape of the scuta, carina, and more especially of the triangular latera, in the form of the peduncle, with its irregularly-scattered calcified scales, in the shape of the animal's body, in the structure both of the mandibles and maxillæ, in the arrangement of the spines, both on the anterior and posterior cirri, Scalpellum villosum most closely resembles, or rather is identical with, Pollicipes. Had it not been for the formation of the valves forming the capitulum, and from the presence of Complemental Males, I should have placed this species alongside of Pollicipes spinosus and sertus. In not having caudal appendages, S. villosum differs from all the species of Scalpellum and Pollicipes; but this organ is variable to an unusual degree in Pollicipes. COMPLEMENTAL MALE. Pl. VI, fig. 4. From the kindness of Professor Owen, Mr. Gray, and Mr. Cuming, I have been enabled to examine six specimens of this species; and on two of them I found Complemental males. They were attached in the same position as in S. Peronii; namely, beneath the adductor muscle, in the fold between the scuta, so as to be protected by the latter when closed. This parasite is six-valved, and has a close general resemblance with that of S. Peronii, but differs in very many points of detail. It is represented of the natural size at _á fig. 4. The capitulum is 43/1000ths of an inch, measured across the scuta and terga; and the same measured from the base of the carina to the top of the capitulum; hence it is broader, by a quarter of the above measurement, and considerably higher than the male of S. Peronii. From the capitulum being higher, that is, not so much truncated, the orifice is placed more obliquely. The membrane connecting the valves is finely villose, and is besides furnished with spines, conspicuously thicker and longer than those on the male S. Peronii. The scuta and terga are much more elongated, a scutum being here 35/1000ths of an inch in length. The carina descends only just below the basal points of the terga, instead of far below them. The rostrum is a little broader and more arched than the carina; it is 2/1000ths in length, and therefore more than two thirds of the length of the carina, the latter being 28/1000ths of an inch from the apex to the basal margin. The primordial valves, with the usual hexagonal tissue, are seated on the tips of the scuta, terga, and carina, but not on the rostrum; so that these valves follow the same law of development, as in the ordinary and hermaphrodite form of Scalpellum. The scuta (a, fig. 4, greatly enlarged), the terga (b), and carina (c) of the male, resemble the same valves in the hermaphrodite, much more closely than do these valves in the male and hermaphrodite S. Peronii. The rostrum has not its basal margin hollowed out, and is very much larger relatively to the carina, than in the hermaphrodite. The large relative size of the rostrum in the complemental male both of this species and of S. Peronii, is a remarkable character, which I can in no way account for. The peduncle is narrow and short, but in a different degree in the two specimens examined. It is naked. The prehensile antennæ were not in a good state of preservation: the disc is narrower than the basal segment, and only slightly pointed, in which important respect it differs from the same part in the foregoing species; at its distal end, rather on the inner side, there are two or three spines, apparently in place of the excessively minute hairs, which are found at the same spot in some or in all the other species of Scalpellum, and in Ibla: similar strong spines occur in Pollicipes. Unfortunately, for the sake of comparison, I was not able to find the prehensile antennæ in the hermaphrodite S. villosum. Mouth.--Labrum bullate, with teeth on the crest. Palpi blunt, spinose. Mandibles, with three teeth; inferior point rather strongly pectinated. Maxillæ, with a considerable notch under the upper pair of large spines; inferior part of the edge not prominent. Outer Maxillæ, with the spines on the inner edge arranged into two groups. Olfactory orifices tubular and prominent, with some long bristles near their bases. In the mandibles having only three teeth, in the maxillæ being notched and in the lower part not being prominent, and, lastly, in the bristles on the inner face of the outer maxillæ being arranged in two groups, these several organs differ from those in the hermaphrodite. Cirri.--First pair short, with only three or four segments in each ramus: second cirrus, with the basal segments not very thickly clothed with spines: sixth cirrus with seven segments, not protuberant in front, each bearing four pairs of spines, without intermediate tufts. Caudal appendages, none. This is an interesting fact, considering that these organs are likewise absent in the hermaphrodite S. villosum,--an absence highly remarkable, and confined to the genus Conchoderma and the one species of Anelasma. Penis thick, not tapering, rather exceeding in length the pedicel of the sixth cirrus, square at the end, and furnished with some spines. In one specimen, I believe I distinguished the vesiculæ seminales: if so, they contained only pulpy matter, and not spermatozoa. There were no ovarian tubes within the peduncle, which was lined by the usual muscles; I traced the two delicate cement-ducts, running from within the antennæ close up to the animal's body. Hence in this case, as in that of S. Peronii, I dare positively affirm that ovarian tubes do not occur; for it is out of the question that I could have traced the cement-ducts, and, at the same time, overlooked the far larger and more conspicuous ovarian tubes, into which, moreover, the ducts, had they existed, would have run. Consequently, these parasites are not females; but judging from the probosciformed penis, and from the presence, as I believe, of vesiculæ seminales, they are males. The complemental males of the present species, and of S. Peronii, so closely resemble each other, that what I have stated regarding the affinities of the latter, are here quite applicable. It is singular how much more alike the parts of the mouth and the cirri of these two complemental males are, than the corresponding parts in the two hermaphrodites: this no doubt is due to the two males having been arrested in their development, at a corresponding early period of growth. Several of the characters, by which the hermaphrodite S. villosum so closely approaches, and almost blends into the genus Pollicipes,--such as the thicker cirri, with the intermediate tufts of bristles, the small second tooth of the mandibles, and the little brush-like prominence on the maxillæ,--are not in the least apparent in the complemental male. SUMMARY ON THE NATURE AND RELATIONS OF THE MALES AND COMPLEMENTAL MALES, IN IBLA AND SCALPELLUM. Had the question been, whether the parasites which I have now described, were simply the males of the Cirripedes to which they are attached, the present summary and discussion would perhaps have been superfluous; but it is so novel a fact, that there should exist in the animal kingdom hermaphrodites, aided in their sexual functions by independent and, as I have called them, Complemental males, that a brief consideration of the evidence already advanced, and of some fresh points, will not be useless. These parasites are confined to the allied genera Ibla and Scalpellum; but they do not occur in Pollicipes,--a genus still more closely allied to Scalpellum; and it deserves notice, that their presence is only occasional in those species of Scalpellum which come nearest to Pollicipes. In the genera Ibla and Scalpellum, the facts present a singular parallelism; in both we have the simpler case of a female, with one or more males of an abnormal structure attached to her; and in both the far more extraordinary case of an hermaphrodite, with similarly attached Complemental males. In the two species of Ibla, the complemental and ordinary males resemble each other, as closely as do the corresponding hermaphrodite and female forms; so it is with two sets of the species of Scalpellum. But the males of Ibla and the males of Scalpellum certainly present no special relations to each other, as might have been expected, had they been distinct parasites independent of the animals to which they are attached, and considering that they are all Cirripedes having the same most unusual habits. On the contrary, it is certain that the animals which I consider to be the males and complemental males of the two species of Ibla, if classed by their own characters, would, from the reasons formerly assigned, form a new genus, nearer to Ibla than to the parasites of Scalpellum: so, again, the assumed males of the three latter species of Scalpellum would form two new genera, both of which would be more closely allied to Scalpellum, than to the parasites of Ibla. With respect to the parasites of the first three species of Scalpellum, they are in such an extraordinarily modified and embryonic condition, that they can hardly be compared with other Cirripedes; but certainly they do not approach the parasites of Ibla, more closely than the parasites of Scalpellum; and in the one important character of the antennæ, they are identical both with the parasitic and ordinary forms of Scalpellum. That two sets of parasites having closely similar habits, and belonging to the same sub-class, should be more closely related in their whole organisation to the animals to which they are respectively attached, than to each other, would, if the parasites were really distinct and independent creatures, be a most singular phenomenon; but on the view that they differ only sexually from the Cirripedes on which they are parasitic, this relationship is obviously what might have been expected. The two species of Ibla differ extremely little from each other, and so, as above remarked, do the two males. In Scalpellum the species differ more from each other, and so do the males. In this latter genus the species may be divided into two groups, the first containing S. vulgare, S. ornatum and S. rutilum, characterised by not having a sub-carina, by the rostrum being small, by the constant presence of four pair of latera, and by the peculiar shape of the carinal latera; the second group is characterised by having a sub-carina and a large rostrum, and may be subdivided into two little groups; viz., S. rostratum having four pairs of latera, and S. Peronii and villosum having only three pairs of latera: now the males, if classed by themselves, would inevitably be divided in exactly the same manner, namely, into two main groups,--the one including the closely similar, sack-formed males of S. vulgare, ornatum, and rutilum, the other the pedunculated males of S. rostratum, Peronii, and villosum; but this latter group would have to be subdivided into two little sub-groups, the one containing the three-valved male of S. rostratum, and the other the six-valved males of S. Peronii and S. villosum. It should not, however, be overlooked, that the two main groups of parasites differ from each other, far more than do the two corresponding groups of species to which they are attached; and, on the other hand, that the parasitic males of S. Peronii and S. villosum resemble each other more closely, than do the two hermaphrodite forms;--but it is very difficult to weigh the value of the differences in the different parts of species. Besides these general, there are some closer relations between the parasites and the animals to which they are attached; thus the most conspicuous internal character by which Ibla quadrivalvis is distinguished from I. Cumingii, is the length of the caudal appendages and the greater size of the parts of the mouth; in the parasites, we have exactly corresponding differences. Out of the six species of Scalpellum in their ordinary state, S. ornatum is alone quite destitute of spines on the membrane connecting the valves; and had it not been for this circumstance, I should even have used the presence of spines as a generic character; on the other hand, S. villosum, in accordance with its specific name, has larger and more conspicuous spines than any other species. In the parasites we have an exactly parallel case; the parasite of S. ornatum being the only one without spines, and the spines on the parasite of S. villosum being much the largest! This latter species is highly singular in having no caudal appendages, and the parasite is destitute of these same organs, though present inn the parasites of S. rostratum and S. Peronii. Again, S. villosum approaches, in all its characters, very closely to the genus Pollicipes, and the parasite in having prehensile antennæ, with the disc but little pointed, and with spines at the further end, departs from Scalpellum and approaches Pollicipes! Will any one believe that these several parallel differences, between the Cirripedial parasites and the Cirripedes to which they are attached, are accidental, and without signification? yet, this must be admitted, if my view of their male sex and mature be rejected. One more, and the most important special relation between the parasites and the cirripedes to which they are attached, remains to be noticed, namely that of their prehensile larval antennæ. I observed the antennæ more or less perfectly in the males of all, and except in S. villosum, in all the species, though so utterly different in general appearance and structure, I found the peculiar, pointed, hoof-like discs, which are confined, I believe, to the genera Ibla and Scalpellum. In the hermaphrodite forms of Scalpellum, I was enabled to examine the antennæ only in two species, S. vulgare and S. Peronii, (belonging, fortunately, to the two most distinct sections of the genus,) and after the most careful measurements of every part, I can affirm that, in S. vulgare, the antennæ of the male and of the hermaphrodite are identical; but that they differ slightly in the proportional lengths of their segments, and in no other respect, from these same organs in S. Peronii,--in which again the antennæ of the male and of the hermaphrodite are identical. The importance of this agreement will be more fully appreciated, if the reader will consider the following table, in which the generic and specific differences of the antennæ in the Lepadidæ, as far as known to me, are given. These organs are of high functional importance; they serve the larva for crawling, and being furnished with long, sometimes plumose spines, they serve apparently as organs of touch; and lastly, they are indispensable as a means of permanent attachment, being adapted to the different objects, to which the larva adheres. Hence the antennæ might, _à priori, have been deemed of high importance for classification. They are, moreover, embryonic in their nature; and embryonic parts, as is well known, possess the highest classificatory value. From these considerations, and looking to the actual facts as exhibited in the following table, the improbability that the parasites of S. vulgare and S. Peronii, so utterly different in external structure and habits one from the other, and from the Cirripedes to which they are attached, should yet have absolutely similar prehensile antennæ with these Cirripedes, appears to me, on the supposition of the parasites being really independent creatures, and not, as I fully believe, merely in a different state of sexual development, insurmountably great. The parasites of S. vulgare take advantage of a pre-existing fold on the edge of the scutum, where the chitine border is thicker; and in this respect there is nothing different from what would naturally happen with an independent parasite; but in S. ornatum the case is very different, for here the two scuta are specially modified, before the attachment of the parasites, in a manner which it is impossible to believe can be of any service to the species itself, irrespectively of the lodgment thus afforded for the males. So again in S. rutilum, the shape of the scutum seems adapted for the reception of the male, in a manner which must be attributed to its own growth, and not to the pressure or attachment of a foreign body. Now there is a strong and manifest improbability in an animal being specially modified to favour the parasitism of another, though there are innumerable instances in which parasites take advantage of pre-existing structures in the animals to which they are attached. On the other hand, there is no greater improbability in the female being modified for the attachment of the male, in a class in which all the individuals are attached to some object, than in the mutual organs of copulation being adapted to each other throughout the animal kingdom.

Generic Characters of the larval prehensile ANTENNÆ, in the Lepadidæ, as far as known from their imperfect state of preservation, and the number of species examined.

 
      |Name of Species.
      |    |Length of, from end of disc to the further margin of the
      |    |oblique basal articulation: Scale, fractions of the 1/6000ths
      |    |of an inch.
      |    |    |Length of, from end of disc to the inner margin of the
      |    |    |basal articulation. Scale same.
      |    |    |    |Width of basal segment, in widest part. Scale same.
      |    |    |    |    |Disc, length of. Scale same.
      |    |    |    |    |    |Disc, width of. Scale same.
      |    |    |    |    |    |    |Ultimate segment, length of. Scale
      |    |    |    |    |    |    |same.
      |    |    |    |    |    |    |    |Ultimate segment, width of.
      |    |    |    |    |    |    |    |Scale, fractions of the
      |    |    |    |    |    |    |    |1/20,000ths of an inch.

LEPAS: disc large, thin, almost circular, slightly elongated, with several long spines on the hinder margin; end segment with three very long, plumose spines on the upper exterior angle.[61]

 
      |L. anatifera (?)
      |    |62
      |    |    |--
      |    |    |    |20
      |    |    |    |    |23
      |    |    |    |    |    |22
      |    |    |    |    |    |    |--
      |    |    |    |    |    |    |    |--

      |L. australis,
      |    |111
      |    |    |--
      |    |    |    |40
      |    |    |    |    |42
      |    |    |    |    |    |39
      |    |    |    |    |    |    |18
      |    |    |    |    |    |    |    |30

      |L. pectinata,
      |    |51
      |    |    |--
      |    |    |    |23
      |    |    |    |    |16
      |    |    |    |    |    |14
      |    |    |    |    |    |    |9
      |    |    |    |    |    |    |    |16

      |L. fascicularis,
      |    |60
      |    |    |40
      |    |    |    |22
      |    |    |    |    |16
      |    |    |    |    |    |15
      |    |    |    |    |    |    |--
      |    |    |    |    |    |    |    |--

DICHELASPIS: disc small, thin, circular, with several spines on the hinder margin; end segment, with two long spines on the upper exterior angle.

 
      |D. Warwickii,
      |    |54
      |    |    |--
      |    |    |    |11
      |    |    |    |    |7-8
      |    |    |    |    |    |7-8
      |    |    |    |    |    |    |6
      |    |    |    |    |    |    |    |13-14

CONCHODERMA: disc large, thin, transversely elongated, with several long spines on the hinder margin; end segment, with two excessively long, plumose spines on the upper exterior corner.

 
      |C. virgata,
      |    |82
      |    |    |40
      |    |    |    |28
      |    |    |    |    |25
      |    |    |    |    |    |35
      |    |    |    |    |    |    |12
      |    |    |    |    |    |    |    |26

      |C. aurita.
      |    |--
      |    |    |--
      |    |    |    |--
      |    |    |    |    |28
      |    |    |    |    |    |40
      |    |    |    |    |    |    |11
      |    |    |    |    |    |    |    |26

ALEPAS: disc small, slightly elongated, with two or more spines on the hinder margin; end segment, with two long spines on the upper inner corner, and four shorter ones on the exterior corner.

      |A. cornuta,
      |    |60
      |    |    |--
      |    |    |    |24
      |    |    |    |    |14
      |    |    |    |    |    |12
      |    |    |    |    |    |    |8
      |    |    |    |    |    |    |    |20

IBLA (parasitic males of): disc, hoof-like, pointed, elongated, with a single spine on the hinder margin; end segment, with four short spines on the upper exterior corner.

 
      |I. Cumingii,
      |    |22
      |    |    |--
      |    |    |    |7-8
      |    |    |    |    |7
      |    |    |    |    |    |--
      |    |    |    |    |    |    |3-4
      |    |    |    |    |    |    |    |7-8

      |I. quadrivalvis,
      |    |32-33
      |    |    |--
      |    |    |    |10
      |    |    |    |    |8
      |    |    |    |    |    |5
      |    |    |    |    |    |    |4
      |    |    |    |    |    |    |    |8

SCALPELLUM: disc hoof-like, generally pointed and elongated, with a single spine on the hinder margin; end segment, with a notch on the inner[61] side, bearing two spines, longer than on the exterior corner.

 
      |S. vulgare,
      |    |39
      |    |    |19
      |    |    |    |10
      |    |    |    |    |10-11
      |    |    |    |    |    |5-6
      |    |    |    |    |    |    |6
      |    |    |    |    |    |    |    |7

      |S. ornatum,
      |    |36
      |    |    |21
      |    |    |    |10
      |    |    |    |    |12
      |    |    |    |    |    |--
      |    |    |    |    |    |    |--
      |    |    |    |    |    |    |    |--

      |S. Peronii,
      |    |30
      |    |    |19
      |    |    |    |--
      |    |    |    |    |9
      |    |    |    |    |    |6
      |    |    |    |    |    |    |5
      |    |    |    |    |    |    |    |10

POLLICIPES: disc small, hoof-like, not pointed, with a single spine on the hinder margin; end segment, as in Scalpellum.

 
      |P. cornucopia,
      |    |20
      |    |    |--
      |    |    |    |6
      |    |    |    |    |6
      |    |    |    |    |    |6
      |    |    |    |    |    |    |6
      |    |    |    |    |    |    |    |8

[61] In the diameter of the disc, the thin membranous border, which is present in the first three genera, is included; but I have some doubts, whether this border be not the first rim of cementing tissue, as all the specimens, of which measurements are here given, had been removed after attachment. In using the terms inner and outer sides of the end segment, it is supposed, that this segment is stretched straight forwards, instead of being bent rectangularly outwards, as in its natural position; and then there can be no doubt which is the inner and outer sides.

It should be observed that the evidence in this summary is of a cumulative nature. If we think it highly, or in some degree probable,--from the ordinary form of Ibla Cumingii having been shown on good evidence to be exclusively female,--from the absence of ova and ovaria in the assumed males of both species of Ibla, at the period when their vesiculæ seminales were gorged with spermatozoa,--from the close general resemblance between the parts of the mouth in the parasites and in the Iblas to which they are attached,--from the differences between the two parasites being strictly analogous to the differences between the two species of Ibla,--from the generic character of their prehensile antennæ,--and from other such points,--if from these several considerations, we admit that these parasites really are the males of the two species to which they adhere, then in some degree the occurrence of parasitic males in the allied genus Scalpellum is rendered more probable. So the absolute similarity in the antennæ of the males and hermaphrodites both in S. vulgare and S. Peronii; and such relations as that of the relative villosity of the several species in this same genus, all in return strengthen the case in Ibla. Again, the six-valved parasites of S. Peronii and S. villosum are so closely similar, that their nature, whatever it may be, must be the same; hence we may add up the evidence derived from the identity of the antennæ in the parasite and hermaphrodite S. Peronii, with that from the antennæ in the male S. villosum, approaching in character to Pollicipes, to which genus the hermaphrodite is so closely allied; and to this evidence, again, may be added the singular coincident absence of caudal appendages in the male and hermaphrodite S. villosum. If these two six-valved parasites be received as the complemental males of their respective species, no one, probably, will doubt regarding the nature of the parasite of S. rostratum, in which the direct evidence is the weakest; but even in this case, the particular point of attachment, and the state of development of the valves, form a link connecting in some degree, the parasites of the first three species with the last two species of Scalpellum, in accordance with the affinities of the hermaphrodites. When first examining the parasites of S. rostratum, S. Peronii, and S. villosum, before the weight of the cumulative evidence had struck me, and noting their apparent state of immaturity, it occurred to me that possibly they were the young of their respective species, in their normal state of development, attached to old individuals, as may often be seen in Lepas; this, however, would be a surprising fact, considering that S. rostratum and S. Peronii are ordinarily attached, in a certain definite position, to horny corallines, and considering that the exact points of attachment in these three parasites, (of which I have seen no other instance amongst common Cirripedes,) namely, between the scuta, would inevitably cause their early destruction, either directly or indirectly, by their living supports being destroyed. Nevertheless, I carefully examined a young specimen of S. rostratum only thrice as large as the parasite; and not having very young specimens of S. Peronii and villosum, I procured the young of closely-allied forms, namely, of S. vulgare, (with a capitulum only 4/100th of an inch in length,) and of Pollicipes polymerus, (with a capitulum of less size than that of one of the parasites,) and there was not the least sign of anything abnormal in the development of the valves. In S. vulgare, at a period when the calcified scuta could have been only 1/100th of an inch in length, (and therefore considerably less than the scuta in the parasites,) the upper latera must have been as much as 4/1000ths of an inch in length, and the valves of the lower whorl certainly distinguishable. To sum up the evidence on the sex of the parasites, I was not able to discover a vestige of ova or ovaria in the two male Iblas; and I can venture to affirm positively, that the parasites of S. Peronii and S. villosum are not female. On the other hand, in the two male Iblas, I was enabled to demonstrate all the male organs, and I most distinctly saw spermatozoa. In the parasitic complemental male of S. vulgare, I also most plainly saw spermatozoa. In the parasites of S. rostratum, S. Peronii, and S. villosum, the external male organs were present. I may here just allude to the facts given in detail under Ibla, showing that it was hardly possible that I could be mistaken regarding the exclusively female sex of the ordinary form of I. Cumingii, seeing how immediately I perceived all the male organs in the hermaphrodite I. quadrivalvis; and as the parasite contained spermatozoa and no ova, the only possible way to escape from the conclusion that it was the male and I. Cumingii the female of the same species, was to invent two hypothetical creatures, of opposite sexes to the Ibla and its parasite, and which, though Cirripedes, would have to be locomotive! I insisted upon this alternative, because if the parasite of I. Cumingii be the male of that species, then unquestionably we have in I. quadrivalvis a male, complemental to an hermaphrodite,--a conclusion, as we have seen, hardly to be avoided in the genus Scalpellum, even if we trust exclusively to the facts therein exhibited. With respect to the positions of the parasitic males, in relation to the impregnation of the ova in the females and hermaphrodites, it may be observed that in the two male Iblas, the elongated moveable body seems perfectly adapted for this end; in the males of the first three species of Scalpellum, the spermatozoa, owing to the manner in which the thorax is bent when protruded, would be easily discharged into the sack of the female or hermaphrodite; this would likewise probably happen with the complemental male of S. rostratum, considering its position within the orifice of the capitulum, between the mouth and the adductor scutorum muscle. The males of S. Peronii and villosum being fixed a little way beneath the orifice of the sack, below the adductor muscle, are less favorably situated, but the spermatozoa would probably be drawn into the sack by the ordinary action of the cirri of the hermaphrodite, and therefore would at least have as good a chance of fertilising some of the ova, as the pollen of many dioecious plants, trusted to the wind, has of reaching the stigmas of the female plants. Regarding the final cause, both of the simpler case of the separation of the sexes, notwithstanding that the two individuals, after the metamorphosis of the male, become indissolubly united together, and of the much more singular fact of the existence of Complemental males, I can throw no light; I will only repeat the observation made more than once, that in some of the hermaphrodites, the vesiculæ seminales were small, and that in others the probosciformed penis was unusually short and thin. Viewing the parasitic males, in relation to the structure and appearance of the species to which they belong, they present a singular series. In S. Peronii and S. villosum, the internal organs have the appearance of immaturity; the shape of the capitulum is specially modified for its reception between the scuta of the hermaphrodite, and several of the valves have not been developed. This atrophy of the valves, is carried much further in S. rostratum. In Ibla, many of the parts are embryonic in character, but others mature and perfect; some parts, as the capitulum, thorax, and cirri, are in a quite extraordinary state of atrophy; in fact, the parasitic males of Ibla consist almost exclusively of a mouth, mounted on the summit of the three anterior segments of the 21 normal segments of the archetype crustacean. In the males of the first three species of Scalpellum, some of the characters are embryonic,--as the absence of a mouth, the presence of the abdominal lobe, and the position of the few existing internal organs; other characters, such as the general external form, the four bead-like valves, the narrow orifice, the peculiar thorax and limbs, are special developments. These three latter parasites, certainly, are wonderfully unlike the hermaphrodites or females to which they belong; if classed as independent animals, they would assuredly be placed not in another family, but in another Order. When mature they may be said essentially to be mere bags of spermatozoa. In looking for analogies to the facts here described, I have already referred to the minute male Lerneidæ which cling to their females,--to the worm-like males of certain Cephalopoda, parasitic on the females,--and to certain Entozoons, in which the sexes cohere, or even are organically blended by one extremity of their bodies. The females in certain insects depart in structure, nearly or quite as widely from the Order to which they belong, as do these male parasitic Cirripedes; some of these females, like the males of the first three species of Scalpellum, do not feed, and some, I believe, have their mouths in a rudimentary condition; but in this latter respect, we have, amongst the Rotifera, a closely analogous case in the male of the Asplanchna of Gosse, which was discovered by Mr. Brightwell[62] to be entirely destitute of mouth and stomach, exactly as I find to be the case with the parasitic male of S. vulgare, and doubtless with its two close allies. For any analogy to the existence of males, complemental to hermaphrodites, we must look to the vegetable kingdom. Finally, the simple fact of the diversity in the sexual relations, displayed within the limits of the general Ibla and Scalpellum, appears to me eminently curious; we have (1st) a female, with a male (or rarely two) permanently attached to her, protected by her, and nourished by any minute animals which may enter her sack; (2d) a female, with successive pairs of short-lived males, destitute of mouth and stomach, inhabiting two pouches formed on the under sides of her valves; (3d) an hermaphrodite, with from one or two, up to five or six similar short-lived males without mouth or stomach, attached to one particular spot on each side of the orifice of the capitulum; and (4th) hermaphrodites, with occasionally one, two, or three males, capable of seizing and devouring their prey in the ordinary Cirripedial method, attached to two different parts of the capitulum, in both cases being protected by the closing of the scuta. As I am summing up the singularity of the phenomena here presented, I will allude to the marvellous assemblage of beings seen by me within the sack of an Ibla quadrivalvis,--namely, an old and young male, both minute, worm-like, destitute of a capitulum, with a great mouth, and rudimentary thorax and limbs, attached to each other and to the hermaphrodite, which latter is utterly different in appearance and structure; secondly, the four or five, free, boat-shaped larvæ, with their curious prehensile antennæ, two great compound eyes, no mouth, and six natatory legs; and lastly, several hundreds of the larvæ in their first stage of development, globular, with horn-shaped projections on their carapaces, minute single eyes, filiformed antennæ, probosciformed mouths, and only three pair of natatory legs; what diverse beings, with scarcely anything in common, and yet all belonging to the same species!

[62] 'Annals of Natural History,' vol. ii, (2d series, 1848,) p. 153, Pl. vi. Mr. Dalrymple has published a very interesting paper on the same subject in the 'Philosophical Transactions,' (p. 342,) 1849; and there is another Memoir by Mr. Gosse in the 'Annals of Natural History,' vol. vi, (1850,) p. 18.

_

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