11. Lithotrya

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_ Genus--LITHOTRYA. Pl. VIII, IX.

LITHOTRYA. G. B. Sowerby. Genera of Shells, April 1822. LITHOLEPAS. De Blainville. Dict. des Scienc. Nat., 1824. ABSIA.[65] Leach. Zoological Journal, vol. ii, July 1825. BRISNÆUS et CONCHOTRYA. J. E. Gray. Annals of Philosophy, vol. x, (new series,) August 1825. LEPAS. Gmelin. Systema Naturæ, 1789. ANATIPA. Quoy et Gaimard. Voyage de l'Astrolabe, 1832. [65] The description of Absia is so inaccurate, that I should not have recognised it, had not the Lithotrya Nicobarica, in a bottle in the British Museum, borne this name.

Valvæ 8, si inter eas parvum (sæpe rudimentale) rostrum et duo parva latera numerentur; incrementi lineis concinnè crenatis: pedunculus squamis calcareis parvis vestitus, in verticillis superioribus crenatis; aut calyci basali calcareo aut discorum ordini affixus. Valves 8, including a small, often rudimentary rostrum and a pair of small latera: lines of growth finely crenated. Peduncle covered with small calcareous scales, those of the upper whorls crenated; attached either to a basal calcareous cup, or to a row of discs. Body lodged within the peduncle: mandibles with three teeth, the interspaces being pectinated; maxillæ various: olfactory orifices slightly prominent: caudal appendages multiarticulate.

Lodged in cavities, bored in calcareous rocks, or shells, or corals; generally within the Tropics.

Description.--The capitulum is not much compressed, a horizontal section giving an oval figure; it is placed obliquely on the peduncle, the scuta descending lower than the terga and carina. There are eight valves, of which the scuta, terga, and carina are large; the rostrum and a pair of latera are very small and often rudimentary. These three latter valves are essentially distinguished from the scales of the peduncle, the upper ones of which they sometimes hardly exceed in size, by not being moulted at each period of exuviation. The latera overlie the carinal half of the terga; I presume that they are homologous with the carinal latera in Scalpellum. Each successive layer of shell forming the valves is thick, and extends over nearly the whole inner surface; hence the carina and terga, and to a certain extent the scuta, either actually do project freely much beyond the sack, or would have done so, had not their upper ends been removed; for the upper and old layers of shell, in most of the species, either scale off or disintegrate and wear away. A rectangularly projecting rim, serrated by small teeth, is formed at the bottom of each fresh layer of growth, along the external surfaces of each valve (see upper part of fig. 1 b´ Pl. VIII.) This structure, as well as that of the crenated scales on the peduncle, is important, for by this means the animal, as we shall presently see, forms and enlarges the cavity in the rock or shell in which it is imbedded. The scutum overlaps either about one third or even one half of the entire width of the tergum, and abuts against a prominent longitudinal ridge on its exterior surface. In L. truncata and L. Valentiana, this ridge on the tergum being folded over towards the scutum, forms a conspicuous furrow, receiving the tergal margin of the latter. In L. Valentiana, there is a second furrow on the carinal side of the tergum, receiving the upper end of the corium-covered or growing surface of the carina. Besides these provisions for holding together the valves, there are, apparently, others for a similar purpose; thus in each scutum, under the rostral angle, there is a roughened knob-like tooth, which touches the under side of the little rostrum, and no doubt serves to give attachment to the membrane uniting the three valves together. In some species, the adjoining basal margins of the scuta and terga, where touching each other, are inflected and roughened; again in L. Rhodiopus, the carinal angles of the terga are produced into points, and in L. truncata and L. Valentiana into prominent roughened knobs, which touch two corresponding small knobs, on the upper part of the growing surface of the carina. Moreover, considerable portions of the inner surfaces of the scuta and terga, are roughened with minute sharp, imbricated points, apparently for the firmer attachment of the corium. The roughened knobs at the rostral angles of the scuta, no doubt are homologous with the teeth in a similar position on one or both scuta in Lepas, and in some fossil species of Pollicipes, as in P. validus. The other projections and roughened surfaces are peculiar to Lithotrya. The growth of all the valves is, as in Pollicipes, simply downwards. The Scuta are triangular, with their umbones or centres of growth at the apex; the tergal margin, as seen from within, is either nearly straight or much hollowed out, accordingly as the scuta simply overlap the terga, or are received in a furrow. In some of the species there is a distinct pit for the adductor muscle, and in others this cannot be distinguished. Terga.--These present great differences in shape; but all appear to be modifications, (as seen internally,) of a rhomboidal figure, which seems to be the normal form of the terga in the Lepadidæ. Of the lower part of the valve, the whole exterior surface, with the exception of a narrow ridge running from the apex down to the basal angle, is hidden by the overlapping of the scuta, latera, and carina. The Carina, in outline is triangular, with the basal margin in some species extremely protuberant. In the first four species, the internal surface is concave, in L. truncata and L. Valentiana it is convex, with a central raised ridge, and consequently the upper freely-projecting portion of the valve, has a prominent central crest or ridge; in L. Nicobarica and L. Rhodiopus there is only a trace of this ridge. The rostrum, as before stated, is always very small; it, as well as the latera, are most developed in L. Nicobarica, and least in L. truncata and L. Valentiana; generally only a few zones of growth are preserved, and from their being enlarged at their basal serrated rims, the rostrum sometimes appears like a few beads of a necklace strung together. The Latera are remarkable from being placed over the carinal half of the terga, in an oblique position, parallel to the lower carinal margin of the terga. A section, parallel to the growth layers, varies in the different species from elliptic to broadly oval, and in L. Nicobarica it is triangular. Only a few layers of growth are ever preserved. In L. truncata, where the latera are represented by mere stiles, (like strings of beads), and are even less in width than the rostrum, they are imperfectly calcified. Microscopical Structure of the Valves.--The shelly layers are white, and generally separate easily, so that in L. dorsalis it is rare to find a specimen with the upper part of the valves perfect. The valves are so translucent, that in the thin margins, even the tubuli could be sometimes distinguished. The valves are coated by strong yellow membrane, which, after the shelly matter in L. dorsalis had been dissolved in acid, separated into broad slips, answering to each zone of growth. On the lower margin of each slip, there is a row of closely approximate spines, generally slightly hooked, pointed, 1/650th of an inch in length, and 1/10000th of an inch in diameter; they arise out of a little fold; all are furnished with tubuli of the same diameter with themselves, running through the whole thickness of the shelly layers, and attached, apparently, by their apices, to the underlying corium. As the spines are very numerous, so are the parallel rows of tubuli. After the shelly layers had been dissolved, there was left in L. dorsalis (well seen in the latera), an extraordinary, conferva-like mass of branching, jointed, excessively thin tubes, sometimes slightly enlarged at the articulations, and appearing to contain brown granular matter: other portions of the valves, instead of this appearance, exhibited membranes or films with similar, branching, articulated tubes or vessels attached to them: I have not seen this appearance in any other cirripede. The yellow exterior enveloping membrane, with its spines, is present in all the species of the genus; in L. Rhodiopus these spines are much larger than in L. dorsalis, and on the inner sides of the carina they are trifid and quadrifid, and large enough to be conspicuous with a lens of weak power. Peduncle.--The most remarkable fact concerning this part, is that the outer tunic, together with the calcareous scales with which it is covered, is moulted at each successive period of exuviation and growth. I demonstrated this fact in L. dorsalis and L. truncata, by removing the old tunic and finding a new membrane with perfect calcified scales beneath; and as these two species, (I obtained, also, pretty good evidence in L. Nicobarica,) are at the opposite extremes of the genus, no doubt this fact is common to the whole genus. I know of no other instance, amongst Cirripedia, in which calcified valves or scales are moulted. I am not certain that the whole skin of the peduncle is thrown off in a single piece; though this almost certainly is the case with the uppermost and lowest portions. The animal's body is partly lodged within the peduncle, which is generally from one to three times as long as the capitulum, and in the upper part is fully as broad as it. The scales with which it is clothed, extend up in the triangular interspaces between the basal margins of the valves. The scales of the upper whorl, or of the two or three upper whorls (Pl. VIII, figs. 1 b´ and 3 d) are larger than those below; and these latter rapidly decrease in size, so as to become low down on the peduncle, almost or quite invisible to the naked eye. The scales in each whorl, are placed alternately with those in the whorls, above and below. All the upper scales are packed rather closely together; those in the uppermost row are generally nearly quadrilateral; those in the few next succeeding whorls, are triangular, with their basal margins protuberant and arched; the scales, low down on the peduncle, stand some way apart from each other, and generally consist of simple rounded calcareous beads, of which some of the smallest in L. dorsalis were only 1/400th of an inch in diameter. In the lowest part of the peduncle these scales, after each fresh exuviation, are apparently soon worn entirely away by the friction against the sides of the cavity; hence in most specimens this part of the peduncle is quite naked. This same part, however, is furnished with nail- or rather star-headed little projections of hard, yellow, horny chitine (fig. 3 e). The star on the summit seems generally to have about five irregular points; one star which I measured was 7/6000th of an inch in total width, the footstalk being only 2/6000th of an inch in diameter; the whole projected 10/6000ths of an inch above the surface of the peduncle; from the footstalk a fine tubulus runs through the membrane to the underlying corium. These star-headed little points are often much worn down; in one specimen which was on the point of exuviation, there remained, in the lower part, close above the basal calcareous cup, only some hard, smooth, yellow, little discs, on a level with the general surface of the membrane,--these being the intersected or worn down footstalks, with every trace of the calcareous beads gone. But in this same specimen, under the old peduncular membrane, there was a new one, studded with the usual circular calcareous beads, slightly unequal in size, generally about 1/400th of an inch in diameter, and each furnished with a tubulus; but as yet none of the star-headed points of chitine had been formed. I believe that these latter are developed from the tubuli leading to the calcified beads, and, therefore, are formed directly under them. In L. cauta the lowest scales on the peduncle are a little larger than in L. dorsalis, giving a frosted appearance to it, and all of them are serrated (fig. 3 d) round their entire margins. Generally only the scales in the uppermost, or in the three or four upper rows are serrated, and this only on their arched and protuberant lower margins. The state of the serrated edge varies extremely in the same species, from elongated conical teeth to mere notches, according to the amount of wear and tear the individual has suffered since the last period of exuviation; so also do the teeth or serrated margins on the valves of the capitulum. Each scale has a fine tubulus passing from the corium through the membrane of the peduncle to its bluntly-pointed imbedded fang or base. The membrane is transparent, thin, and tender, to a degree I have not seen equalled in the other Lepadidæ, except, perhaps, in Ibla. It is much wrinkled transversely. Muscles of the Peduncle.--These consist of the usual interior and longitudinal,--exterior and transverse--and oblique fasciæ; the former are unusually strong; downwards they are attached to the basal calcareous cup or disc, and upwards they extend all round to the lower curved margins of the valves. They are, as usual, without transverse striæ. Besides these, there are, (at least in L. dorsalis and L. Nicobarica,) two little fans of striæ-less muscles, which occur in no other pedunculated cirripede; they are attached on each side of the central line of the carina, near its base; they extend transversely and a little upwards, and each fan converges to a point where the lower margins of the carina and terga touch; of these muscles, the upper fasciæ are the longest. Their action, I conceive, must be either to draw slightly together the basal points of the terga, and so serve to open their occludent margins, or to draw inwards the base of the carina: these muscles apparently first shadow forth the posterior or carinal, transversely-striated, opercular muscles of sessile cirripedes. Basal Calcareous Cup or Discs.--I have seen this part in all the species, except L. Valentiana, and in this it probably occurs, considering its very close alliance with L. truncata. The size, form, and conditions of the cup or disc varies infinitely according to the age, size, and position of the individual specimen. We will commence with a full-sized animal, which has ceased to burrow downwards into the rock, in which case the discs usually grow into a cup, and become largely developed. In L. dorsalis alone, I have seen many specimens, so that the following description and remarks, though applicable I believe to all the species, are drawn up from that alone. The cup (Pl. VIII, fig. 1 a´, 1 c´) is hardly ever regular in outline, and is either slightly or very deeply concave; I have seen one, half an inch in diameter; it is formed of several thick layers of dirty white, translucent, calcareous matter, with sinuous margins; externally the surface is very irregular, and is coated by yellow membrane presently to be described. The innermost and last-formed layer sometimes covers the whole inside of the cup, and extends a little beyond its margin all round; but more generally it projects beyond only one side, leaving the other sides deserted. I have seen a single new layer extending beyond the underlying old layers, as much as one sixth of an inch; and again I have seen a part of the cup, as much as a quarter of an inch in width, deserted and covered with serpulæ. So irregular, however, is the growth, that after a period an old deserted portion will occasionally be again covered by a new layer, though of course without organic adhesion. Again it sometimes happens that the last-formed layer, remaining central, is very much less than the older layers; in one such instance the innermost and last-formed layer (fig. 1 a´) had a diameter of only a quarter of that of the whole cup, in the middle of which it was placed; the cup thus tends to become filled up in the middle. The cup, in its fully developed condition, is seated at the very bottom of the cavity in the rock. From the aggregate thickness of the several component layers forming the cup, the old and mature animal rises a little in its burrow; for instance, the bottom of the cup in one specimen which I measured, was 4/10ths of an inch in thickness. In a younger condition, before the animal has bored down to the full depth, and whilst the cavity is only of moderate diameter, the lower part of the peduncle, instead of being attached to the inside of a cup, adheres to small, irregular, nearly flat, calcareous discs, overlapping each other like tiles (figs. 1, 2 a´). They are placed one below the other, generally in a straight line, and are attached firmly to one side of the burrow. The discs are oval, or rounded, or irregular, and are commonly from 1/20th to 1/10th of an inch across: they usually form a quite straight ribbon, widening a little downwards: each little disc overlaps and extends beyond the one last formed, fully half its own diameter. I have seen one row of discs an inch in length, but the upper discs are always worn away by the friction of the calcified serrated scales on the peduncle. It is very important to observe that the lowest disc is not fixed, (as was the case with the cup,) at the very bottom of the burrow, but on one side, just above the bottom, which latter part is occupied by the blunt basal end of the peduncle. In a valuable paper on L. Nicobarica, by Reinhardt, presently to be referred to, the disc is said to be attached on the carinal side (see fig. 2) of the peduncle; and this, I believe, is general. I have seen one instance in which, during the excavation of a new burrow, an old burrow was met with, and the row of discs turned down it, making, with their previous course, nearly a right-angle. In another similar instance, the discs, instead of turning down, became very large and broad, and so fairly formed a bridge across the old burrow (fig. 1),--becoming narrow again as soon as the animal recommenced burrowing into the solid rock. Sometimes, as it appears, the animal, whilst still small, from some unknown cause, stops burrowing downwards, and then a cup is formed at the bottom of the hole. As soon as the animal has got to its full depth, the burrow increases only in diameter, and during this process the linear row of discs is ground away and lost; a cup is then formed. The little discs can be deposited or formed only at each fresh exuviation; and as some of the burrows are above two inches in depth, and as on an average each disc does not extend beyond the underlying disc more than 1/15th of an inch, an animal which has bored two inches in depth, must have moulted at least thirty times. I may here remark that I have reason to believe, from some interesting observations made by Mr. W. Thompson, of Belfast, that some sessile cirripedes moult about every fortnight. Internal Structure of the Cup.--When the cup is dissolved in acid, each shelly layer is represented by a rather tough, pale-brown membrane, itself composed of numerous fine laminæ, which, under a one-eighth of an inch object glass, exhibit generally only the appearance of a mezzotinto drawing; but there often were layers of branching vessels, (like moss-agate,) less than the 1/10,000th of an inch in diameter, and of a darkish colour; these vessels are not articulated, but otherwise resemble the same peculiar structure in the valves of the capitulum. The exterior yellow membrane is marked, or rather composed of successive narrow rims, which, in fact, are the lines of termination of the laminæ of membrane, which in a calcified state form the cup itself. In most parts, both on the borders and under the centre of the cup, but not everywhere, there are imbedded in the yellow membrane, elongated, irregular, top-shaped masses of bright yellow chitine, each furnished with a tubulus, which penetrating the calcareous laminæ leads to the corium; the little apertures thus formed, are clearly visible in the layers of membrane, left after exposure to acid. In L. Nicobarica, the innermost shelly layer of the cup was punctured, like the surface of the shell in Chthamalus and many other sessile Cirripedes, by the internal orifices of these tubuli. The top-shaped masses often have star-shaped summits; and they differ in no essential respects from those on the lower part of the peduncle, excepting that they are quite imbedded in the membrane covering the under surface of the cup, whereas those on the peduncle project freely. I found these top-shaped bodies in the outer membrane of the cups in L. dorsalis, L. cauta, and L. Rhodiopus, which alone I was enabled to dissolve in acid; and I mention this fact, as indicating the probable presence of the more important star-headed projections on the lower parts of the peduncle in these same species. The basal calcareous cup resembles, in essential structure, the valves of the capitulum; the chief difference being that in the former there is a larger proportion of animal matter or membranous layers. After the dissolution of the cups, in L. dorsalis and L. Rhodiopus, I most distinctly traced the two cement-ducts; they included the usual darker chord of cellular matter; they were of rather small diameter, namely, 2/3000th of an inch. The two (in L. dorsalis) ran in a very irregular course, not parallel to each other, making the most abrupt bends. They passed through the membranous layers, (as seen after dissolution,) and running for short spaces parallel to the component laminæ, were attached to them. In their irregular course, these cement-ducts resemble those of Pollicipes mitella, but I could not perceive that any cement had been poured out at the abrupt bends. In one specimen of a basal cup, which I was enabled to examine whilst still attached to the rock, I found under the very centre, (and of course outside the yellow membrane,) a very small area of dark brown cement of the usual appearance. In several specimens of full-sized cups, I was not able to perceive any cement on the external surfaces of the upper and later-formed layers; hence I believe that the cup is cemented to the bottom of the hole only during the early stages of its formation; and this, considering its protected situation, would no doubt be sufficient to affix the animal. This probably accounts for the small size of the cement-ducts, and for the facility with which, as it appears, the cups can be removed in an unbroken condition from the rock. In the case, however, of the small, flat, calcareous discs, which are formed whilst the animal is burrowing into the rock, these are attached firmly to the sides of the holes, in the usual manner, by cement. In this cirripede it would be useless to look for the prehensile antennæ of the larva under the cup, for the animal, during the formation of the successive discs, must have travelled some distance from the spot on which the larva first attached itself. The membrane of the peduncle is continuous with the yellow membrane coating the external surface of the cup; and this latter membrane is continuous with those delicate laminæ which, in a calcified condition, form the layers of the cup itself. In an exactly similar manner, in this and other cirripedes, the membrane of the peduncle, at the top, is continuous with that coating the valves, and is attached to the lower exterior edge of the last-formed layer of shell. When a new shelly layer is formed, both under the valves of the capitulum and inside the basal calcareous cup, it projects beyond the old layer, and is included within the old, as yet not moulted, membrane of the peduncle. Within the cup of L. Nicobarica I found a lately-formed layer of shell, projecting 1/10th of an inch on one side of the cup, and by its protuberance distinguishable even through the old coat of the peduncle, which was nearly ready to be moulted. In an analogous manner, in the capitulum of L. dorsalis and L. truncata, I have found a new peduncular membrane bearing the usual, but then sharp, calcified scales, attached to the lower projecting edge of the last-formed shelly layer, lying under the old peduncular membrane, which was attached to the penultimate layer of shell, and with its worn scales was just ready to be moulted. The final cause of the moulting of the calcified scales, together with the membrane of the peduncle to which they are attached,--a case confined to Lithotrya,--I have scarcely any doubt is the reproduction of a succession of scales, sharply serrated for the purpose of enlarging the cavity in which the animal is lodged. The extreme thinness of the membrane of the peduncle has been noticed; this may be partly related to its protected condition, but partly, I think, to the necessity of its being formed in a very extensible condition; for the new coat, owing to the projection of the new shelly layers under the valves, and within the basal cup, is by so much shorter than the old peduncle, yet after exuviation it has to stretch to a greater length than the old membrane, to allow of the growth of the Cirripede. Owing to the thinness and fragility of this membrane, the basal attachment of the Cirripede is, no doubt, chiefly effected by the unusually strong longitudinal muscles; and the necessity of a surface of attachment for these muscles, stronger than the external membrane of the peduncle, probably is one of the final causes of the basal calcareous disc and cup, and likewise for the unusual manner in which the valves of the capitulum are locked together by folds and small roughened projections. The basal discs and cup, however, apparently serve for several other purposes, namely, for raising the animal a little in its burrow, (which is narrow and pointed at the bottom,) at that period of growth when it has ceased to burrow downwards, but still increases in diameter; also for carrying the animal, as over a bridge, across any pre-existing cavity in the rock; and lastly, perhaps, for removing lower down, in the intervals of exuviation, the point of attachment for the longitudinal peduncular muscles. Position of the animal in the rock, and its power of excavation.--A specimen of rock, two or three inches square, in Mr. Cuming's possession, is full of Lithotryas; the cavities extend in every possible direction, and several were parallel, but with the animals in reversed positions; the same thing is apparent in some specimens of Mr. Stutchbury's, and it was evident that the positions occupied by the animals were entirely due to chance. In Mr. Cuming's specimen of rock, a considerable portion of the external surface is preserved, and here it can be seen that many of the specimens have their capitulums directed from the external surface directly inwards. These individuals, which were of full size, must have preyed on infusoria inhabiting the cavities of the porous, calcareous rock. On the other hand, I have seen some young specimens of L. dorsalis with their valves not at all rubbed, and others of full size with uninjured Balani and corallines on the tips of the valves, and again a specimen of L. truncata with minute pale-green sea-weed on the summit of the capitulum,--all which appearances induce me to believe that in these cases, the valves had projected freely beyond the cavity in which their peduncles were lodged. I may here also mention that in Mr. Cuming's specimen, above alluded to, the basal cups of five specimens touched and adhered to each other; I was not able to make out whether there had originally existed separate burrows, as I think is most probable, and that the walls had been wholly worn away, or whether the five specimens had fixed themselves on one side of a large pre-existing, common cavity. Young specimens seem to burrow to the full depth, before nearly acquiring the diameter which they ultimately attain. I measured one burrow, 1.2 of an inch in depth, which, at its mouth or widest part, was only .17 in diameter. The several species occur imbedded in soft calcareous rocks, in massive corals, and in the shells of mollusca and of cirripedes. It has been doubted by several naturalists, whether the basal calcareous cup at all belongs to the Lithotrya, but after the foregoing microscopical observations on its structure, it is useless to discuss this point. So again it has been doubted whether the cavity is formed by the cirripede itself; but there is so obvious a relation between the diameters of specimens of various sizes, and the holes occupied by them, that I can entertain no doubt on this head. The holes, moreover, are not quite cylindrical, but broadly oval, like the section of the animal. The simple fact, that in this genus alone each fresh shelly layer round the bases of the valves, and therefore at the widest part of the capitulum, are sharply toothed; and secondly, that in this genus alone a succession of sharply serrated scales, on the upper and widest part of the peduncle, are periodically formed at each exuviation; and that consequently the teeth on the valves and scales are sharp, and fit for wearing soft stone, at that very period when the animal has to increase in size, would alone render the view probable that the Lithotrya makes or at least enlarges the cavities in which it is imbedded. Although it may be admitted that Lithotrya has the power of enlarging its cavity, how does it first bore down into the rock? It is quite certain that the basal cup is absolutely fixed, and that neither in form nor state of surface it is at all fitted for boring.[66] I was quite unable to answer the foregoing question, until seeing the admirable figures by Reinhardt[67], (Pl. VIII, figs. 2 and 2 a´) of L. Nicobarica, still attached in its cavity. Subsequently I obtained from Mr. Stutchbury several pieces of rock completely drilled with holes, many of small diameter, by L. dorsalis, and in these I found numerous instances of the linear rows of little discs, like those of L. Nicobarica, showing in the plainest manner, that each time a new disc is formed, that is, at each exuviation, the animal moves a short step downwards; and as the lowest of these little discs in none of the burrows was placed at the very bottom, we see that the lowest point of the peduncle must be the wearing agent. In the peduncle of an individual of L. dorsalis, nearly ready to moult, I found, it may be remembered, beneath and round the basal disc, under the old membrane of the peduncle, a new membrane studded with calcified beads, but with the horny star-headed spines not yet developed, whilst on the old outer coat these latter had been worn down quite smooth, and the calcified beads worn entirely away. Here, then, we have an excellent rasping surface. With respect to the power of movement necessary for the boring action, the peduncle is amply furnished with transverse, oblique, and longitudinal striæ-less muscles,--the latter attached to the basal disc. In all the pedunculata, I have reason to believe that these muscles are in constant slight involuntary action. This being the case, I conceive that the small, blunt, spur-like portion of the peduncle, descending beneath the basal rim of the lowest disc, would inevitably partake slightly of the movements of the whole distended animal. As soon as the Lithotrya has reached that depth, which its instinct points out as most suitable to its habits, the discs are converted into an irregularly growing cup, and the animal then only increases in diameter, enlarging its cavity by the action of the serrated scales on the peduncle, and of the serrated lower edges of the valves of the capitulum. With respect to those reversed individuals attached with their capitulums downwards, I suppose that the larvæ had crept into some deep cavity, perhaps made originally by a Lithotrya, of which the rock in the specimen in question was quite full, and had there attached themselves. Finally, it appears that in Lithotrya the burrowing is simply a mechanical action; it is effected by each layer of shell in the basal attached discs overlapping, in a straight line, the last-formed layer,--by the membrane of the peduncle and the valves of the capitulum having excellent and often renewed rasping surfaces,--and, lastly, by the end of the peduncle (that is homologically the front of the head) thus roughened, extending beyond the surface of attachment, and possessing the power of slight movement.

[66] Mr. Hancock, in his admirable account of his burrowing Cirripede, Alcippe lampas, ('Annals of Nat. Hist.,' Nov. 1849, p. 313,) came to this conclusion regarding the cup of Lithotrya, and hence was led to think that this genus did not form its own burrows, but inhabited pre-existing cavities. I am much indebted to this gentleman, who has been so eminently successful in his researches on the boring powers of marine animals, for giving me his opinion on several points connected with the present discussion. [67] I owe to the great kindness of Prof. Steenstrup the sight of this Plate, published in the 'Scientific Communications from the Union of Natural History,' Copenhagen, January 30, 1850, No. I. Since this sheet has been set up in type, I have received from Prof. Steenstrup the memoir, in Danish, belonging to the figures in question; and the greater part of this has been translated to me by the kindness of a friend. My account of the means of burrowing is essentially the same as that published by Reinhardt; but the moulting of the scales on the peduncle, the presence of scales and of points of a different nature, the method of attachment by cement, the conversion of the discs into a cup, &c., seem not to have been known to this naturalist. Reinhardt states that the points on the peduncle will scratch Iceland spar, and that, apparently, they are formed of phosphate of lime: in the case of the closely-allied L. dorsalis, I must believe that the scales or beads on the peduncle are formed of carbonate of lime, for they were quickly dissolved with effervescence in acetic acid; and the star-headed points, which are subsequently developed under the calcareous scales, appeared to me, under the compound microscope, to be formed of a horn or chitine substance. Reinhardt states that the basal point of the peduncle is arched a little under the lowest disc, and there forms for itself a slight furrow (as represented in the lateral view, Pl. VIII, fig. 2); but in the burrows examined by me, this furrow or depression did not really exist, the appearance resulting from the basal margin of the lowest disc, projecting beyond the wall of the cavity by the amount of its own slight thickness.

* * * * * We will now proceed with our generic description.-- Animal's Body.--This, as already stated, is partially lodged within the peduncle. The prosoma is rather largely developed. The Mouth is placed at a moderate distance from the adductor muscle. The Labrum is moderately bullate, with a row of blunt bead-like teeth, mingled with fine bristles, on the crest, which in the middle part is generally somewhat flattened. The Palpi are blunt, and even squarely truncated at their ends; they are of large size, so that, if they had been half as large again, or even less, their tips would have met. Mandibles (Pl. X, fig. 2), with three nearly equal large teeth, and the inferior angle produced, broad, and strongly pectinated: in the interspaces between these teeth there are, in all the species, some very fine teeth or pectinations, which are seated a little on one side of the medial line. The mandibles are somewhat singular from the size of the transparent flexible apodemes (a a) to which the muscles are attached; these are oval and constricted at their origins: in L. dorsalis they are roughened with little points; in L. cauta and L. truncata they are large, of the same shape, but smooth. Maxillæ.--These are larger, compared to the mandibles, than is usual with pedunculated Cirripedes; they differ in shape in the different species, being either nearly straight on their edge, and notched or not (fig. 10), or notched with the inferior part forming a double prominence (fig. 12); the spines on the inferior angle, which is sometimes slightly produced, are always crowded together into a brush, and are finer than those on the upper parts. The apodemes are less straight than is usual, and at their origin take, in all the species, a rather abrupt bend; their extremity is enlarged into a little disc, which in L. dorsalis is covered with strong points, but in the other species is, as usual, smooth. Outer Maxillæ.--The inner margin is slightly concave, and in L. truncata alone, the bristles are hardly continuous, being interrupted in the middle part. The olfactory orifices are only very slightly prominent. The spines on all the trophi are more or less doubly serrated. Cirri.--The three posterior pair are elongated, with their anterior surfaces not at all protuberant. The segments bear from three to five pair of spines, with a row of three or four small intermediate spines; there are, as usual, some little lateral upper rim spines; the dorsal tufts contain some thick and thin spines mingled. First cirrus is short, and placed not quite close to the second pair; the basal segments are broad and thickly paved with bristles. The second pair is rather short compared with the third pair; a varying number of the basal segments in both rami of both these cirri are protuberant, and are thickly paved with bristles; such segments are more numerous and are broader on the anterior rami than on the posterior rami. In L. cauta alone, none of the basal segments in the posterior rami of the second and third cirri are thickly paved with bristles. The pedicels of the first three pair are irregularly covered with spines; those of the three posterior pair have the spines arranged in a regular double line. Most of the spines are doubly serrated. Caudal Appendages (Pl. X, fig. 23 and 24), multiarticulate, with thin elongated segments fringed with short spines; in length generally exceeding the pedicel of the sixth cirrus, and in L. Nicobarica equalling half the entire length of this cirrus. Stomach, destitute of cæca; oesophagus somewhat curled. Filamentary Appendages, none. Ovaria filling up the peduncle and surrounding the sack, but not extending up to the bases of the scuta and terga; I saw the ova only in L. truncata; they were here oval and large, being nearly 9/400ths of an inch in length. Penis, elongated; vesiculæ seminales extending into the prosoma. I noticed the ovigerous fræna only in L. truncata; here they were large, with an almost bilobed outline; the margin and whole lateral surface being covered with elongated cylinders, finely pointed, but not enlarged at their extremities, as are the glands observed in most of the other genera. Colours.--The posterior thoracic segments, the pedicels, the anterior and dorsal surfaces of the segments of the cirri, the caudal appendages, and the outer sides of the trophi are, in most of the species, more or less mottled with dark purple; parts of the interior surfaces of the valves in some of the species are coloured fine purple. Geographical Distribution.--The species are found all round the world in the tropical seas; this fact may have some connection with the presence of soft coral-reef limestone and of massive corals in these seas. The presence, however, of L. cauta on the shores of New South Wales, shows that the genus is not strictly tropical. Affinities.--Lithotrya is a well-pronounced distinct genus; although there is a considerable difference in the shape of the valves between L. dorsalis and L. Valentiana, at the opposite extremes of the genus, the strict uniformity of the internal characters shows that there are no grounds whatever for any generic separation; moreover, L. Rhodiopus neatly blends together these extreme forms. Indeed it is not easy to imagine a better marked series of transitional forms, than those presented by the terga, in passing from L. dorsalis through L. Nicobarica, L. Rhodiopus, and L. truncata, to L. Valentiana. Lithotrya has most affinity to Scalpellum villosum or to Pollicipes spinosus and P. sertus; though the affinity is far from close. In these two species of Pollicipes, we have seen that large irregular calcified spines are formed at the base of the peduncle, whereas in the other Pedunculata the scales or spines are formed exclusively round the upper margin of the peduncle. Lithotrya, as has been remarked by Sowerby and other authors, exhibits some affinity to the sessile Cirripedes, as shown by the calcareous basis,--by the manner in which the scuta and terga are locked together,--by the two little fans of muscle attached to near the basal points of the terga,--and perhaps by some of the characters of the trophi; nevertheless, this affinity is far from being well-marked, and I think is hardly so plain as in Pollicipes mitella. 1. LITHOTRYA DORSALIS. Pl. VIII, fig. 1 a´.

LITHOTRYA DORSALIS. G.B. Sowerby. Genera of Shells, April, 1822. LEPAS DORSALIS. Ellis. Nat. Hist. Zoophytes, Tab. xv, fig. 5, 1786. LITHOLEPAS DE MONT SERRAT. De Blainville. Dict. des Sc. Nat., Plate, fig. 5, 1824.

L. scutis terga angustè obtegentibus: carinâ intùs concavâ: rostro, duorum aut trium squamarum subjacentium latitudinem æquante: lateribus, squamarum quinque subjacentium longitudinem æquantibus, superficie internâ angustè ellipticâ: pedunculi squamis superioribus verticillum secundum minus duplo superantibus. Scuta, narrowly overlapping the terga: carina internally concave: rostrum as wide as two or three of the subjacent scales: latera with their internal surfaces narrowly elliptical, as long as five of the subjacent scales: upper scales of the peduncle less than twice as large as those in the second whorl. Mandibles, with twice as many pectinations between the first and second main teeth, as between the second and third teeth. Maxillæ without a notch, edge nearly straight, and spines very numerous: caudal appendages exceeding, by half, the length of the pedicel of the sixth cirrus.

Barbadoes, West Indies; Venezuela; Honduras; imbedded in limestone; Mus. Brit. Cuming and Stutchbury.

The state of preservation of the valves in different specimens varies greatly; generally only two or three, or even only the last-formed shelly layer, is preserved, the upper ones having scaled off; in a few young specimens, however, all the layers were perfect. The carina is generally better preserved than the other valves, and hence the upper part usually projects freely; in one specimen no less than ten zones of growth were preserved in the carina, whilst the other valves consisted of only three: the terga generally project rather more than the scuta. As each growth-layer is thick, if the scaling process had not taken place, all the valves would have projected greatly. The little teeth lie close together on the prominent serrated rims, on each zone of growth. The internal surfaces of the valves are roughened with small imbricated points. Exteriorly the valves are covered with yellow membrane, with rows, corresponding with each zone of growth, of very minute, yellow, horny spines, generally having their tips bent over, and so made hook-shaped. These spines are less than 1/600th of an inch in length. Scuta, triangular; internally concave, with a large depression for the adductor muscle; there is the usual small roughened internal knob, or tooth, at the rostral angle of both the right and left hand valves. Tergal margin straight, overlapping about one third of the entire width of the terga. Terga, irregularly oval, with the scutal margin straight; basal point blunt, with the two sides placed at about an angle of 45° to each other; the lower part of the carinal margin, immediately over the latera, (as seen internally,) is slightly hollowed out. Exteriorly, towards the bottom of the valve, from the overlapping of the scuta, of the latera, and of the carina, only a narrow rounded ridge is exposed, which runs down to the basal angle at about one third of the entire width of the valve, from the scutal margin. Internally the valve is slightly concave. The Carina slightly overlaps the terga; internally concave; generally with a large upper portion freely projecting; inwardly curved, without any central crest or ridge; valve nearly as wide as the middle part of the terga; inner growing or corium-covered surface, with its basal margin, protuberant and arched. Rostrum (Pl. VIII, fig. 1 a´, a, and greatly magnified 1 b´) very narrow; rarely more than two or three layers of growth are preserved; the sides are deeply sinuous, owing to each zone widening downwards; basal margin rounded; in width equalling about two and a half of the uppermost scales of the peduncle, and about half as wide as the latera. Latera, small, placed obliquely, and parallel to the lower carinal margin of the terga; longer axis equal to five of the uppermost scales of the peduncle, and to nearly half the width of the base of the carina; growing surface (or a section made parallel to the growth-layers,) is narrow, elliptic, pointed at both ends, but the carinal half rather thicker than the scutal half. The Peduncle varies in length, generally about twice as long as the capitulum, in one specimen above thrice as long. The upper part as wide as the capitulum, the lower part sometimes much attenuated. The calcified scales in the uppermost whorl (Pl. VIII, fig. 1 b´) are only slightly larger than those in the second whorl; the scales in the succeeding three or four whorls, are considerably larger than those below, which latter very gradually decrease in size, till, low down on the peduncle, they are barely visible to the naked eye. In this lower part, they may be called calcareous beads; they stand some way apart from each other; they are nearly hemispherical, smooth, translucent, and furnished with a conical fang; some of the smallest were 1/325th and 1/400th of an inch in diameter. The upper scales vary somewhat in the outline, the most usual shape being sub-triangular, with the lower margin arched and protuberant; and this margin, in the two or three upper whorls, is crenated with teeth, which are conical and sharp, after exuviation, but soon become reduced to mere notches. The scales in the uppermost whorl are usually nearly quadrilateral; the imbedded portion, or fang of each scale, is, in all, produced into a blunt rounded point. The basal calcareous cup (fig. 1 a´ and 1 c´) is well developed, and is sometimes even half an inch in diameter. Before the cup is formed, there is a row of small, flat discs (fig. 1, and like those in fig. 2 a´) attached to the sides of the burrow: but a full account of these parts of the peduncle, and of the burrowing habits of this species, has been given under the generic description. Size and Colour.--Full average-sized specimens have a capitulum half an inch in width and height; the entire length, with the contracted peduncle, being about an inch and a half. Valves coloured dirty white, with the enveloping membrane, when preserved, yellow. The outer maxillæ, palpi, pedicels of the cirri, anterior faces of the segments, dorsal tufts, caudal appendages, and penis, dark purple. Thoracic segments brown. There is a purple spot between the bases of the first pair of cirri. Mouth.--Labrum considerably bullate, equalling about half the longitudinal diameter of the mouth; inferior part produced so as to separate the mouth some way from the adductor muscle; crest with a row of blunt teeth and hairs; central part depressed and flattened. Palpi, rather large, separated from each other by only half their own length; bluntly pointed, thickly clothed with spines. Mandibles (Pl. X, fig. 2), with twice as many pectinations, namely 15, between the first and second main teeth, as between the second and third teeth, namely about 7; inferior angle strongly and coarsely pectinated; distance between the tips of the first and second main teeth, considerably less than between the tips of the second tooth and of the inferior angle; sides hirsute. Maxillæ (fig. 10), with the edge not quite straight, with the whole inferior part slightly projecting; spines very numerous, thirty or forty pairs; those close beneath the two upper great unequal spines, form a tuft and are rather thinner than the others, as are also those near the inferior angle; sides hirsute. Outer Maxillæ, rather pointed, with the inner edge slightly concave, continuously and thickly clothed with short spines; spines on the outer edge long; there are also some minute, short, thinly scattered spines or points on the sides. Bristles on all the trophi doubly serrated. Cirri.--The first pair is placed at a small distance from the second. The segments in the three posterior pairs, support five pairs of very long spines, with a row of (I believe) four small intermediate spines; on the lateral upper edges, there are some short blunt spines; anterior faces of the segments not protuberant; the dorsal tufts consist of thick serrated, and of thin spines. The whole integument is hirsute with minute pectinated scales. Two or three of the basal segments in the sixth cirrus are confluent. First cirrus, anterior ramus rather shorter and thicker than the posterior ramus; basal segments thickly paved with serrated spines; in the posterior ramus, the six terminal segments are not paved with bristles. Second cirrus has the seven basal segments of the anterior ramus very broad, and paved with bristles; the eight terminal segments having the usual structure; in the posterior ramus the three or four basal segments are similarly paved, but to a very much less degree, and the remaining thirteen have the usual structure. Third cirrus has the six basal segments of the anterior ramus very broad and paved, and the fourteen terminal ones of the usual structure; in the posterior ramus, the three or four basal segments are similarly paved, but to a very much less degree, and the seventeen terminal ones have the usual structure. The pedicel of the first cirrus has very few spines; those of the second and third cirrus are thickly and irregularly clothed with spines; and those of the three posterior pair have a double row with intermediate small spines. On the antero-lateral faces of the pedicels of the second, third, and fourth pairs of cirri, there is an elongated white swelling or shield. Moreover, on the posterior thoracic segments, there are similar white-coloured swellings, with the membrane more plainly marked with scales than in other parts. The spines on the first three pairs of cirri are coarsely serrated. Caudal Appendages (Pl. X, fig. 23), with numerous tapering segments, almost equalling one and a half times the length of the pedicel of the sixth cirrus. Each segment is elongated and somewhat constricted in the middle, with its upper edge (fig. 24) crowned with short spines; in a full-sized specimen there were seventeen segments. 2. LITHOTRYA CAUTA. Pl. VIII, fig. 3. L. scutis terga amplè obtegentibus: carinâ intus concavâ: rostro squamarum subjacentium latitudinem vix æquante: lateribus, squamas subjacentes sesquitertio superantibus; superficie internâ latè ellipticâ: pedunculi squamis superioribus verticillum secundum pæne quadruplo superantibus. Scuta largely overlapping the terga: carina internally concave: rostrum hardly as wide as one of the subjacent scales: latera with their internal surfaces broadly elliptical, as long as two and a half of the subjacent scales: upper scales of the peduncle nearly four times as large as those in the second whorl. Mandibles with an equal number of pectinations between the first, second, and third main teeth: maxillæ notched, edge nearly straight: posterior rami of the second and third cirri, with their basal segments not paved with bristles: caudal appendages slightly exceeding in length the pedicels of the sixth cirrus.

New South Wales, Australia, imbedded in a Conia, (unique specimen,) Mus. Stutchbury.

Valves thin, white, translucent; upper layers of growth well preserved, excepting on the terga. A large portion of the carina projected freely. The teeth on the projecting margins of the growth-layers are broad, blunt, and often stand rather distant from each other. Scuta (Pl. VIII, fig. 3 a), triangular, internally concave with no distinct pit for the adductor muscle. The scuta largely overlap the terga. Terga (fig. 3 b) approaching to rhomboidal; basal angle rectangular, almost central, and consequently the exterior longitudinal ridge, which is rounded, is likewise nearly central. Carina, internally concave, with no trace of a central internal ridge in the upper free portion; the growing or corium-covered surface is transversely oval, and is as wide as the widest part of the terga. Rostrum, exceedingly minute, enlarged at each zone of growth, not so wide as the immediately subjacent scale on the peduncle. Latera (fig. 3 c), in width equalling two and a half of the upper peduncular scales, or about one fourth or one fifth of the width of the carina; growing surface, (or a section parallel to the layers of growth,) broadly elliptic, pointed at both ends. Peduncle, about twice as long as the capitulum; the scales of the uppermost whorl are quadrilateral (fig. 3 d), and nearly four times as large as those in the second whorl; these latter are about twice as large as those in the third whorl, which are very little larger than the small, almost equal-sized, equally distant, round beads scattered over the rest of the peduncle, down to the basal cup. All these scales are dentated, the upper rows most plainly and only on their basal margins; the lower little beads are very slightly crenated round their entire margins; they are mingled with star-headed spines (fig. 3 e) of yellow chitine. Basal calcareous discs thin, plainly marked exteriorly by concentric lines of growth, and covered by the usual yellow membrane, including the horny, spindle-shaped bodies. Size and Colours.--The whole specimen, including the peduncle, was only one fifth of an inch in length; the capitulum being 3/40ths of an inch in width. I do not know whether the specimen had attained its full size, but think this is probable, as a large-sized species would not have made its habitation in one of the valves of so small a shell as a Conia. Shell white, exterior membrane, where preserved, yellow, and bearing small spines. Thoracic segments, the lower segments of the second, third, and fourth cirri, all the segments of the first cirrus and the trophi, slightly mottled with darkish purple. Mouth.--The teeth or beads on the crest of the labrum are blunt, few, not very small, and equidistant. Palpi, bluntly pointed. Mandibles, with the three main teeth nearly equal in size; the pectinations are equal in number, namely, only three between the first and second, and the second and third main teeth; the inferior angle is coarsely pectinated, with one central spine much longer than the others; the distance between the tips of the first and second main teeth, equals that between the second tooth and the inferior angle. Maxillæ, with the two upper spines very large; beneath them there are two small spines, and a considerable notch; the inferior part of the edge is nearly straight, bearing about thirteen pairs of spines, obscurely divided into two groups, the lower spines being smaller than the upper ones. The upper convex margin is hirsute with long hairs. Outer Maxillæ, blunt, with the inner margin slightly concave; continuously, but thinly clothed with spines. Cirri.--The segments of the three posterior pairs bear four pairs of spines, with the usual intermediate fine spines; dorsal spines thin and thick mingled together. First cirrus, short, with the anterior ramus rather the thickest and shortest; all the segments thickly paved with bristles, except the two terminal segments, of which the ultimate one bears some serrated spines of most unusual length, namely, equalling within one segment the entire length of the ramus. I presume that these spines serve as feelers. Second cirrus; anterior ramus much thicker and considerably shorter than the posterior ramus; six basal segments paved with bristles, the two terminal segments having the usual structure; posterior ramus with all its nine segments on the usual structure. Third cirrus, longer, to a remarkable degree, than the second cirrus, with its anterior ramus having the four basal segments paved, and the seven terminal ones on the usual structure; posterior ramus with twelve segments, of which none are paved. The pedicels of the second and third cirri thickly and irregularly clothed with spines. The upper segments of the pedicels of all the cirri are unusually long. Caudal Appendages, longer than the pedicels of the sixth cirrus, by barely one third of their own length. Segments much elongated, seven in number; I may add for comparison that each ramus of the sixth cirrus contained, in this specimen, sixteen or seventeen segments. General Remarks.--It is difficult to give obvious characters, (excepting the smallness of the rostrum compared with the scales on the peduncle,) by which this species can be externally discriminated from L. dorsalis, L. Nicobarica, and L. Rhodiopus; yet almost all the valves differ slightly in shape. In this species alone, (the peduncle of L. Rhodiopus is not known,) the lower, microscopically minute, bead-like scales of the peduncle are crenated, though obscurely, all round. In the animal's body, the diagnostic characters are strongly marked;--the long spines on the terminal segment of the first cirrus,--none of the segments in the posterior rami of the second and third cirri being thickened and paved with bristles,--the pectinations being equal in number between the main teeth of the mandibles,--are all characters exclusively confined to this species. 3. LITHOTRYA NICOBARICA. Pl. VIII, fig. 2.

L. NICOBARICA. Reinhardt, Naturhist; Selskabet, Copenhagen. No. I. 1850. Tab. I, fig. 1-3.[68] [68] I am not at all sure that the proper title of the periodical in which this species has been described, is here given. I am greatly indebted to Prof. Steenstrup for sending me a separate copy of the paper in question, written in Danish. I believe I am right in identifying the specimen here described, from Timor, with the species from the Nicobar Islands, named by Reinhardt, L. Nicobarica.

L. scutis terga angustè obtegentibus: carinæ cristâ internâ tenui in parte superiore positâ: rostro conspicuo, squamarum sex subjacentium latitudinem æquante: lateribus, superficie internâ triangulâ, squamarum septem subjacentium latitudinem æquantibus. Scuta narrowly overlapping the terga: carina with a slight central internal ridge in the upper part: rostrum conspicuous, as wide as six of the subjacent scales: latera, with their internal surfaces triangular, as wide as seven of the subjacent scales. Palpi square at their ends: mandibles with twice as many pectinations between the first and second main teeth, as between the second and third: maxillæ slightly notched, with the inferior angle slightly prominent: caudal appendages more than twice as long as the pedicels of the sixth cirrus.

Timor; Brit. Mus., (given by Cuvier to Leach); Nicobar Islands, according to Reinhardt.

Capitulum as in L. dorsalis. The teeth on the prominent rims of the valves are small and approximate; but the specimen was much worn. Scuta, triangular, slightly overlapping the terga; the line of junction between these valves slightly sinuous, the upper part of the tergal margin of the scuta being slightly hollowed out, and the corresponding upper portion of the margin of the terga being slightly protuberant. Internally, there is a considerable depression for the adductor muscle; and besides the usual knob at the rostral angle, there is a trace of a knob at the baso-tergal angle. Terga, as seen internally, irregularly rhomboidal, ending downwards in a blunt point, of which the two sides, (neither being sensibly hollowed out,) stand at about an angle of 45° to each other. Scutal margin, with the upper part, (as above remarked,) slightly protuberant: near the bottom of this margin, there is a very slight projection, answering to the small knob at the baso-tergal angle of the scutum. Externally, towards the basal angle, the narrow strip not concealed by the overlapping of the latera and carina is square-edged, with the zones of growth on it straight. Carina, internally concave in the upper free part, with a slight, central, internal crest, caused by the projection of each successive zone of growth. The inner growing surface is almost pentagonal in outline; with the basal margin square and truncated in the middle. Rostrum (fig. 2 a), rather conspicuous, many zones of growth being preserved. It equals in width six of the subjacent scales of the peduncle, but as these are rather smaller than elsewhere, the width equals about five of the ordinary uppermost scales; compared with the latera, it is nearly 5/7ths of their width. Latera, unusually large; as seen on their interior surfaces, (or in a section parallel to the zones of growth,) they are triangular, elongated transversely, with the carinal angle a rectangle. In width they equal the seven subjacent scales of the peduncle, and are more than half as long as the basal margin of the carina. Peduncle, with the upper scales varying from circular to quadrilateral, thrice as large as those in the second whorl; beneath which, in the next three or four whorls, the scales rapidly decrease in size; and beneath these the whole peduncle is studded with equal-sized, rounded, calcareous beads, so minute as to be quite invisible to the naked eye. This specimen was nearly ready to moult, and perhaps in consequence of this, even the upper scales were most obscurely serrated on their lower margins, and all the others quite smooth: there were some much worn horny spines close to the bottom of the peduncle. Basal calcareous cup slightly concave, of moderate size; its diameter, in the one specimen examined, was 9/10ths of an inch; it was composed of several layers. In the specimen figured (2 a´) by Reinhardt, instead of a cup, there is a straight row of small discs, which are attached to the walls of the cavity, as explained in the generic description. Mouth.--Palpi with their ends square and truncated; thickly clothed with long spines. Mandibles, with fully twice as many pectinations, (viz. from 16 to 20,) between the first and second main teeth, as between (viz. 8 to 10) the second and third main teeth. Inferior angle, coarsely pectinated. The distance between the tips of the first and second teeth, is considerably less than between the tip of the second tooth and the inferior angle. Maxillæ, with the edge very slightly irregular; beneath the two great upper spines there is a slight notch, with some small spines: inferior angle slightly prominent, with a brush of moderately fine spines; besides these, there are about seventeen pairs of large spines; sides very hairy. Outer Maxillæ, with the inner margin slightly concave, and with the spines continuous. Cirri.--The segments in the three posterior pairs support three or four pairs of long spines, with a single row of moderately long intermediate spines; the dorsal tufts consist of a few rather thick, and some long and thin spines. The front of the segments is not protuberant; the whole surface is hirsute with minute comb-like scales. Second cirrus, with the anterior ramus having its eight basal segments highly protuberant and thickly clothed with spines, the upper nine having the usual structure; the posterior ramus has four or five basal segments thickly clothed with spines, and the twelve upper ones with the usual structure. Third cirrus, with the anterior ramus having six segments highly protuberant and thickly clothed with bristles, and the fifteen upper ones on the usual structure; in the posterior ramus, only three or four of the basal segments are paved with bristles. The spines on the first three pairs of cirri, are coarsely and doubly serrated. The Caudal Appendages are more than twice as long as the pedicels of the sixth cirrus, and equal half the length of the whole cirrus. In a specimen in which the sixth cirrus contained twenty-two segments, the caudal appendages actually contained twenty. The segments are thin, with their upper edges clothed with serrated spines. The slip of membrane on each side, whence this organ springs is united, for a little space, to the lower segment of the pedicel of the sixth cirrus. Size and Colour.--Width of the capitulum rather above 4/10ths of an inch; length, including the peduncle, (contracted by spirits,) nearly one inch. Valves, as usual, dirty white, partly invested by yellow membrane, furnished with a few minute yellow horny spines. Pedicels of the first four cirri, caudal appendages, penis, the two posterior thoracic segments, the segments of the cirri, and the trophi, clouded, banded, or spotted, with blackish purple. Affinities.--This species, in the characters derived from the valves, comes perhaps nearest to L. Rhodiopus; in the characters derived from the animal's body, it is nearest to L. dorsalis. 4. LITHOTRYA RHODIOPUS. Pl. VIII, fig. 4.

BRISNÆUS RHODIOPUS. J. E. Gray. Annals of Philosoph., vol. x, (new series,) 1825. ---- ---- J. E. Gray. Spicilegia Zoolog., Tab. xvi, fig. 17, 1830.

L. scutis terga ample obtegentibus: carinæ cristâ internâ tenui, in parte superiore positâ: lateribus, superficie internâ symmetricè et latè ovatâ, carinæ latitudinis plus quam tertiam partem æquantibus: tergorum basali apice tenui, et angulo carinali producto: rostro et pedunculo ignotis. Scuta largely overlapping the terga. Carina with a slight central internal ridge in the upper part. Latera with their internal surfaces symmetrically and broadly oval, more than one third of the width of the carina. Terga with the basal points narrow, and the carinal angle produced. Rostrum and peduncle unknown. Mandibles, with four times as many pectinations between the first and second main teeth, as between the second and third; distance greater between the tips of the first and second teeth, than between the tip of the second tooth and the inferior angle. Maxillæ widely notched, with the inferior part forming two obscure prominences.

Hab. unknown. Imbedded in a massive coral. Brit. Mus.

The specimens are in a rather bad condition, and have been disarticulated. They are of rather small size; the rostrum and peduncle are lost, and animal's body much injured. Valves white, thin, translucent; teeth on the projecting rims small, narrow, standing further apart than their own width. The upper layers have undergone but little disintegration or scaling off, and consequently the carina and terga project freely. The valves, where not rubbed, are covered by bright yellow membrane, which is thickly clothed with rows of spines; these are small on the exterior surfaces, but are very large and hooked in certain parts, as near the tergal margins of the scuta, and on the carinal margins of the terga, and especially on the inner face of the upper free part of the carina. Here the hooked spines (fig. 4 d) are trifid or quadrifid, and are very conspicuous. Scuta, as seen externally, triangular; they overlap half the width of the terga; on their internal faces (fig. 4 a), in the upper projecting part, there is a strong ridge, against which the scutal margin of the terga abuts. There is a deep and conspicuous pit for the adductor muscle. Terga, as seen externally, nearly triangular. The ridge which leads from the apex to the basal angle, is rounded, central, and extremely prominent; but does not form a furrow, or include the overlapping margin of the scuta. The basal angle is narrow, spur-like, and slightly hollowed out on both margins. The growing corium-covered surface (fig. 4 b) is transversely elongated, with the occludent margin rounded, and the carinal angle much produced, but not forming a roughened knob. Carina (fig. 4 d), concave within, with a slight central ridge in the upper free portion. The inner growing surface is concave, almost pentagonal, with a just perceptibly raised central rim in the upper part, and with two minute prominences on each side, against which the produced carinal angles of the terga abut. Rostrum, lost. Latera (fig. 4 c), growing surface (or a section parallel to the growth-layers,) symmetrically oval, more than one third as wide as the basal margin of the carina. Several zones of growth preserved. Peduncle, lost, but a few scales accidentally adhering to one of the valves, show that they are crenated in the three or four upper whorls. No basal calcareous cup was preserved, but by clearing out the base of one of the holes in the coral, in which a specimen had been imbedded, I found a little flat disc about the size of a pin's head; it was composed of two or three layers, and was externally coated by yellow membrane, including the usual spindle-shaped bodies and tubuli. The cement-ducts were also discovered after dissolution in acid. So that there could be no doubt regarding the nature of the little disc. Mouth.--Labrum with a row of little blunt teeth. Palpi, blunt, rather expanded at their ends, with the extreme margin much arched and furnished with two rows of long spines; there is a fringe of short spines on the straight inner side. Mandibles.--There are nine pectinations between the first and second main teeth, and only two between the second and third teeth; the inferior angle is coarsely pectinated, with one central spine twice as long as the others. The distance between the tips of the first and second main teeth, is greater than between the tip of the second tooth and the inferior angle. Maxillæ (Pl. X, fig. 12).--These may be described as having their edge formed into three prominences; or, as having a very wide notch under the two upper great spines, and with the whole inferior part forming two prominences. There are, altogether, about twelve pairs of spines, of which two stand singly on the inferior side of the wide notch under the two upper great spines. The spines on the inferior angle are rather smaller than those above; sides hirsute. Outer Maxillæ, with the inner margin slightly concave, and sparingly covered with bristles. Cirri, imperfectly preserved; the three posterior pairs have segments of the usual character, bearing five pairs of very long spines, with the usual little intermediate, the minute lateral, and the dorsal spines. First cirrus lost; second and third with only their few basal segments preserved, sufficient, however, to show that at least two or three segments, in both the anterior and posterior rami of both cirri, were paved with bristles. Pedicels, as in the other species. Caudal Appendages, lost. This species comes very close, as far as the characters derived from the trophi serve, to the L. truncata, though readily distinguished from that species by the shape of the valves. On the other hand, the capitulum of this species is distinguished with difficulty from that of L. Nicobarica and L. cauta; no doubt this difficulty is much enhanced by the rostrum and peduncle having been lost. 5. LITHOTRYA TRUNCATA. Pl. IX, fig. 1.

ANATIFA TRUNCATA. Quoy et Gaimard. Voyage de l'Astrolabe, Pl. xciii, figs. 12 to 15, 1834.

L. scutis in profundam tergorum plicam insertis: carinæ cristâ centrali prominente et rotundatâ in parte superiore: rostro et lateribus rudimentalibus, carinæ latitudinis quindecimam fere partem æquantibus. Scuta locked into a deep fold in the terga: carina with a prominent central rounded ridge in the upper part: rostrum and latera rudimentary, about 1/15th of the width of the carina. Mandibles, with nearly three times as many pectinations between the first and second teeth, as between the second and third teeth; distance between the tips of the first and second teeth equal to that between the tip of the second tooth and inferior angle. Maxillæ widely notched, with the inferior part forming two prominences. Caudal appendages shorter than, or barely exceeding in length, the pedicels of the sixth cirrus.

Friendly Archipelago, Mus. Paris; Philippine Archipelago, Mus. Cuming; imbedded in coral rock.

Capitulum rather thick, with the five main valves having their free apices, diverging and truncated. The upper and old layers of shell do not here scale off so readily as in many of the foregoing species; and hence an unusually large proportional length of each valve projects freely above the sack; and the valves are of unusual thickness. The capitulum is very nearly as wide at its summit as at its base, owing to the divergence of the apices of the valves. The scuta and terga are articulated together by a conspicuous fold, which, when seen from vertically above, (Pl. IX, fig. 1 a´,) appears like a deep wedge-formed notch in the terga. On the exterior surfaces of the valves, the teeth on the successive rims are approximate; on the inner surfaces, the rims are covered by strong yellow membrane, which is generally fringed with small horny spines. Scuta, exterior surface convex, sub-triangular, with the apex truncated: seen vertically from above, there is a small rectangular indentation or fold which receives the projecting scutal margin of the terga. The inner growing or corium-covered surface (fig. 1 b, b´) is triangular, with its tergal margin largely hollowed out. Along the occludent margin there is a slight ridge, which terminates at the rostral angle, in both the right and left-hand valves, in a rounded, knob-like, roughened tooth. The lower part of the tergal margin is slightly inflected and roughened, where it meets the corresponding lower part of the scutal margin of the terga. There is a deep pit for the adductor muscle. The interior surface of the valve above this pit is faintly-coloured purple. The inner surfaces of both scuta and terga, are roughened with little points. Terga, seen externally, are almost quadrilateral (owing to the apex being truncated), with the free margin facing the scutum, arched. Seen vertically from above, each shows a deep fold, which receives the lower part of the tergal margin of the scutum. In the foregoing species, a prominent ridge runs down the exterior surface of the terga from the apex to the basal angle, against which ridge, the margin of the overlapping scuta abuts: here this ridge, instead of projecting straight out, is oblique or folded over, and thus forms a furrow, receiving the margin of the scuta. The interior growing surface of the tergum (fig. 1 b´, c), presents so irregular a figure, that it can hardly be described; in area it quite equals the scuta; it is slightly concave; at the upper point of the carinal margin, there is a large, rounded, protuberant, roughened knob, which corresponds with a small knob on each side of the inner face of the carina; these knobs seem firmly united together by membrane. The scutal margin of the terga, in the upper part, forms a shoulder, largely projecting over the scuta; on its lower part, there is a small roughened projection. The occludent margin is arched and protuberant, with a slight fold above the knob on the carinal margin, just mentioned: this fold is caused by the protuberance of the central internal ridge of the carina, but is so small, that when the capitulum is seen from vertically above, it can hardly be distinguished. Finally, the basal half of the carinal margin, runs in the same line with the basal margin of the scuta. Carina, moderately large; seen externally, the surface presents an elongated triangle, with the apex truncated; on the internal face (fig. 1 b´, d) of the free part, there is (instead of being concave as is usual) a great central ridge, which projects between the diverging apices of the terga, as may be seen from vertically above; hence the thickness of the upper part of the carina, in a longitudinal plane, almost equals its breadth. The edge of this ridge is rounded. The inner or growing surface of the carina is tinted purple, and lies in a plane, oblique to the longer axis of the valve; it is triangular, with the apex cut off, and the basal margin rounded and protuberant; it is not concave. There is a central raised line or slight ridge on this inner surface, and on each side in the upper part there is a small, white, roughened knob, corresponding with the similar knobs on the carinal margins of the terga. Rostrum (fig. 1 b´, a), rudimentary; in one specimen it was about 1/50th of an inch in width; it is either as wide, or only half as wide, as the subjacent scale on the peduncle. Latera, rudimentary, placed between the edges of the carina and the terga; rather smaller than the rostrum; almost cylindrical, slightly flattened, enlarged at each zone of growth, with one or two sharp teeth or spines on both faces; imperfectly calcified; in width barely 1/15th part of the carina. Peduncle, short; the scales alone in the uppermost whorl are plainly toothed; they are transversely elongated, and almost quadrangular, and are nearly twice as large as those in the second whorl. Beneath this second whorl, there are two or three whorls, with scales, graduated in size; and the rest of the peduncle is covered by rather distantly scattered, minute, rounded or acutely pointed scales: the pointed scales are directed upwards, and are best developed under the carina. The basal calcareous cup, judging from two specimens, is thin, and not much developed. Size and Colour.--The largest specimen was nearly 6/10ths of an inch across its capitulum. The calcareous valves are dirty white. The sack is (after having been long kept in spirits) pale coloured, excepting a small purple space, between the scuta and another over the carina. The three posterior segments of the thorax and portions under the second and third cirri, the trophi, the pedicels and the anterior faces of the segments (especially of the basal segments in the second and third cirri), and a spot on their dorsal surfaces, and the penis are all coloured dark purplish-black. The prosoma is pale coloured. Mouth.--Crest of labrum with a row of bead-like teeth and hairs. Palpi bluntly pointed, with neither margin hollowed out. Mandibles, with eight pectinations between the first and second main teeth, and three between the second and third teeth; inferior angle coarsely pectinated, with a central spine much longer than the others; the distance between the tips of the first and second main teeth, is about equal to that between the tip of the second tooth and of the inferior angle. Maxillæ.--Under the two upper long spines (associated with some smaller ones), there is a slight and wide hollow; and the whole inferior edge obscurely forms two blunt points, with the spines on the lower projection smaller than the upper spines. Outer Maxillæ, considerably concave in front, with the spines almost discontinuous in the middle part. Cirri.--First pair rather far separated from the second pair. The segments of the three posterior cirri bear three or four pairs of main spines, and are otherwise characterised like the foregoing species. First cirrus, with its anterior ramus much thicker than the posterior ramus, and of nearly equal length; all the segments, except the two terminal ones, thickly clothed with serrated spines. Second cirrus considerably shorter than the third cirrus: anterior ramus with the seven basal segments very protuberant, and paved with bristles, and the four terminal ones on the usual structure; posterior ramus, with the five basal segments paved (but much less thickly than in the anterior ramus), and the nine terminal ones on the usual structure. Third cirrus, the anterior ramus, with the five basal segments, thick and paved, and eleven terminal segments on the usual structure: posterior ramus, with one basal segment paved, and sixteen other segments on the usual structure. In the posterior rami, however, of both the second and third cirri, it is difficult to draw any distinct line between the paved segments and the others. Caudal Appendages, short, either just exceeding in length the pedicels of the sixth cirrus, or equalling only the lower segment: segments flattened, cylindrical, six in number, there being, in the same individual, twenty-one segments in both rami of the sixth cirrus. 6. LITHOTRYA VALENTIANA. Pl. VIII, fig. 5.

CONCHOTRYA VALENTIANA. J. E. Gray. Annals of Philosoph., vol. x (new series), 1825.

L. scutis in profundam tergorum plicam invertis: tergorum opposito superiore margine, plicâ alterâ æquè profundâ instructo: carinæ cristâ prominente centrali, marginibus quadratis, in parte superiore: rostro rudimentali: lateribus et pedunculo ignotis. Scuta locked into a deep fold in the terga; the latter having a second equally deep fold on the opposite upper margin. Carina with a prominent, central, square-edged ridge in the upper part: rostrum rudimentary. Latera and peduncle unknown. Animal unknown.

Red Sea, imbedded in an oyster-shell. British Museum.

General Remarks.--The two specimens in the British Museum are small, and in an imperfect condition, without the peduncle or the latera, and without the body of the animal. The capitulum so closely resembles that of L. truncata, that it is quite superfluous to do more than point out the few differences. It is just possible, though not probable, that this form may prove to be merely a variety or younger state of L. truncata, in which case this latter name would have to be sunk. The difference, though one only of degree, in the form of the terga of the two species is conspicuous, and there is a slight difference in the carina, and again some dissimilarity in habits. Description.--The valves, as just stated, generally resemble those of L. truncata; scarcely any appreciable difference can be detected in the scuta; the apex, however, of the inner surface seems coloured a darker purple. The terga, as seen from vertically above (Pl. VIII, fig. 5 b), have a fold or indentation on the upper or occludent margin, as large and as conspicuous as that receiving the margin of the scuta: this fold, as seen on the inner corium-covered surface (fig. 5 a), descends below the roughened knob at the upper angle of the carinal margin, which is not the case with the slight fold in the same place in L. truncata; its presence seems caused by the edge of the central internal crest, in the upper part of the carina, being square (instead of round, as in L. truncata), and thus more deeply affecting the outline of the terga, between which it is inserted. The upper part of the scutal margin of the terga, as seen internally (fig. 5 a), overlaps the scuta in a large rectangular projection. From the depth of the two opposite folds, namely, that caused by the tergal edge of the scuta and that by the crest of the carina, the inner face of the tergum is divided into two almost equal areas. The carina has its central crest square (fig. 5 c, d,) instead of being rounded as in L. truncata. The inner growing or corium-covered face is nearly at right angles to the longitudinal axis of the whole valve, instead of being oblique to it; it is convex or protuberant, with a central raised line, and two little knobs on each side of the upper part; the two lateral margins are slightly hollowed out, and the basal margin is not highly protuberant. The rostrum is excessively minute, barely above 1/200th of an inch in width; it is a little enlarged at each zone of growth. Latera lost; no doubt they were rudimentary. A fragment of a posterior cirrus, which adhered to one of the valves, shows that each segment supported four pairs of spines. Width of the capitulum before disarticulation, probably was about 1/10th of an inch. * * * * * Species mihi non satis notæ, aut dubiæ.

ANATIFA VILLOSA. Brugière. Encyclop. Meth. Des. Vers., tom. i, 1789, p. 62, Pl. clxvi. On ships: Mediterranean. ANATIFA HIRSUTA[69] Conrad. Journal of the Acad. of Nat. Sc., Philadelphia, vol. vii, 1837, p. 262. On fuci, Fayal, Azores.

The specimens, to which these names have been given by the above two authors, are described as small, and the A. villosa was suspected by Brugière to be young. The A. hirsuta is said by Conrad to have the valves minutely striated, granulated, and covered by a strong hirsute epidermis; the scuta, compared with the other valves, are very large; the entire length of this specimen was a quarter of an inch. The A. villosa is described as having smooth valves, and apparently the peduncle alone is hirsute. Now, in young individuals of Lepas australis, the peduncle is hairy, whilst in full-grown specimens it is quite smooth. Again, in some varieties of L. fascicularis, the thorax, prosoma, and cirri are hirsute, whereas they are generally quite smooth; hence I am inclined to suspect that A. villosa is the young, in a state of variation, of L. anatifera; and that A. hirsuta bears a similar relation to L. anserifera. In Lamarck's 'Animaux sans Vertèbres,' Pollicipes villosus of Sowerby is quite incorrectly given as a synonym to the above A. villosa.

[69] The Anatifa hirsuta of Quoy and Gaimard is the Ibla quadrivalvis of this work. ANATIFA ELONGATA. Quoy et Gaimard. Voyage de l'Astrolabe, Pl. xciii, fig. 6.

This, I think, is certainly a distinct and new species, but I am unable to decide whether to place it in Lepas or Pæcilasma. It is briefly described and pretty well figured in the above work. It was procured at New Zealand, but it is not stated to what object it was attached. The capitulum is much elongated, and one inch in length; the peduncle is from six to eight lines long. The carina is said to be very narrow; it is not stated whether it terminates downwards in a fork or disc; judging from the figure, it extends some way up between the terga, the basal ends of which are bluntly pointed. The scuta are almost quadrilateral. The peduncle is short, yellow, and tuberculated. The general appearance of the drawing makes me suspect that it is a Pæcilasma.

CLYPTRA. Leach. Zoological Journal, vol. ii, p. 208, July, 1825.

Leach has most briefly characterised a specimen in Savigny's Museum, from the Red Sea, under the above name of Clyptra. It has only four valves, and its peduncle is smooth; by the latter character it is distinguished from Ibla. Apparently this is a distinct and new genus. * * * * * Mr. J. E. Gray, in 'Proc. Zoolog. Soc.,' 1848, p. 44, quotes a description by Stroem ('Nym. Saml. Danske,' 1788, 295, n. iii, f. 20), namely, "Lepas testâ compressâ 7-valvis, stipite lamellosâ." It is found attached to Gorgonia placomus, in the North Sea. I suspect that this is the common Scalpellum vulgare, and that Stroem counted the valves only on one side, overlooking the rudimentary and concealed rostrum; and this would give seven for the number of the valves. Had it not been for the expression "stipite lamellosâ," I should have thought this might have been an unknown species of Dichelaspis.

SCALPELLUM LÆVIS. Risso. Hist. Nat. des Product. de l'Europe Mérid., 1826, Tom. iv, p. 385.

The chief characteristic of this species appears to be indicated by its specific name. It is found in the Mediterranean, attached to Cidarites. I am inclined to believe that it is distinct from S. vulgare.

SCALPELLUM PAPILLOSUM. King. Zoolog. Journal, vol. v, p. 334.

Captain King has described this species, taken from the depth of 48 fathoms, on the coast of Patagonia, in Lat. 44° 30´ S. It is probably distinct, but is so imperfectly described, that not even the number of the valves is given.

POLYLEPAS (POLLICIPES), Sinensis. Chenu. Illust. Conchyliolog., Pl. II, fig. 7.

This species is said to come from China; it is nearest to P. spinosus, but is, I think, distinct.

EXPLANATION OF THE PLATES.


TAB. I.

Fig.

  1. Lepas anatifera, (nat. size.) Var., with a row of square,
        dark-coloured marks on the scuta and terga.

  1a. Lepas anatifera, external view of carina, magnified
        thrice.

  1b. Lepas anatifera, lateral view of carina, magnified thrice;
        var. dentata.

  1c. Lepas anatifera, internal view of right-hand scutum, to
        show the tooth at the umbo.

  2. Lepas Hillii, (nat. size.)

  3. Lepas pectinata, (magnified thrice.)

  3a. Lepas pectinata, var. (spirulæ), tergum, magnified
        thrice.

  4. Lepas anserifera, (nat. size.)

  5. Lepas australis, (nat. size.)

  5a. Lepas australis, carina, external view of, magnified
        twice.

  6. Lepas fascicularis, (nat. size,) with its peduncle, together
        with those of three other specimens, imbedded in a vesicular
        ball of their own formation, of which a slice has been cut
        off to show the internal structure. The specimen is in the
        College of Surgeons.

  6a. Lepas fascicularis, carina of, nat. size.

  6b. Lepas fascicularis, var. villosa.

  6c. Lepas fascicularis, var. villosa, carina of.

  6d. Part of the membrane from one side of the peduncle of Lepas
        fascicularis, with the ball removed, showing one of the
        cement-ducts, and the orifices through which the vesicular
        membrane forming the ball has been secreted; greatly
        magnified; viewed from the outside.


TAB. II.

Fig.

  1. Poecilisma Kæmpferi, (magnified two and a half times.)

  1a. Poecilisma Kæmpferi, carina of.

  2. Poecilisma aurantia, (magnified two and a half times.)

  3. Poecilisma crassa, (magnified twice.)

  3a. Poecilisma crassa, carina of.

  4. Poecilasma fissa, (magnified five times.)

  5. Poecilasma eburnea, (magnified five times.)

  5a. Poecilasma eburnea, carina of, external view of.

  5c. Poecilasma eburnea, carina of, lateral view of.

  5b. Poecilasma eburnea, scutum, internal view of.

  6. Dichelaspis Warwickii, (magnified five times.)

  6a. Dichelaspis Warwickii, transverse section of the top of
        the peduncle, showing the deeply-notched end of the inwardly
        bent carina; magnified five times.

  6b. Dichelaspis Warwickii, var., scutum and tergum.

  7. Dichelaspis pellucida, (magnified five times.)

  7a. Dichelaspis pellucida, basal end of carina of, much
        magnified.

  8. Dichelaspis Lowei, (magnified nearly ten times.)

  8a. Dichelaspis Lowei, fork of carina of, viewed internally.

  9. Dichelaspis Grayii, (magnified eight or nine times.)

  10. Dichelaspis orthogonia, (magnified six times.)

  10a. Dichelaspis orthogonia, carina, lateral view of.

  10b. Dichelaspis orthogonia, basal end of carina, viewed
        internally, much magnified.


TAB. III.

Fig.

  1. Oxynaspis celata, (magnified three times.)

  1a´. Oxynaspis celata, with the skin of the encrusting horny
        zoophyte removed. (a), scutum; (b), tergum; and (c),
        carina.

  2. Conchoderma virgata (magnified twice.)

  2a. Conchoderma virgata carina, viewed externally.

  2b. Conchoderma virgata summit of capitulum, showing the terga
        from vertically above.

  2c. Conchoderma virgata var. chelonophila, (magnified four
        times).

  2d. Conchoderma virgata var. Olfersii, (scutum.)

  3. Conchoderma Hunteri, (magnified five times.)

  4. Conchoderma aurita, (nat. size,) with the rudimentary carina
        exhibited on the right hand.

  4a. Conchoderma aurita, summit of capitulum, viewed from
        vertically above, showing the ear-like appendages and the
        rudimentary terga.

  4b. Conchoderma aurita, section near the bases of the ear-like
        appendages, showing their folds.

  4c. Conchoderma aurita, (var.), scutum.

  5. Alepas minuta, (magnified five times.)

  6. Alepas cornuta, (magnified five times.)


TAB. IV.

Fig.

  1. Anelasma squalicola, (copied from Lovèn.) The ovigerous
        lamellæ are seen within the edges of the aperture of the
        capitulum. Enlarged about one and a half times.

  2. Anelasma squalicola, (from Lovèn), with the membranes removed
        from one side of the capitulum and of the peduncle,
        exhibiting the body.

        (a.) External membrane of the capitulum.

        (a, a.) Inner membrane of ditto, lining the sack, and
          separated from the external membrane by a double fold of
          corium.

        (b.) The ovigerous lamellæ, the edge projecting beyond the
          orifice of the capitulum.

        (c.) Penis, succeeded by six pairs of rudimentary cirri.

        (d.) Probosciformed mouth.

        (e.) Orifice of the acoustic (?) sack.

        (f.) Ovigerous frænum.

        (g.) Ovarian branching tubes filling up the peduncle.

        (h.) Outer integument of peduncle, lined by corium and
          muscles, continuous with the outer membrane (a) of the
          capitulum.

  3. Anelasma squalicola, Small portion of the outer integument
        of the peduncle, greatly magnified, exhibiting the natural
        lines of splitting, and showing that it is composed of
        several distinct portions or layers, which are displayed by
        the corners having been turned over. Three of the branching
        filaments, filled with pulpy corium, are given; the others
        have been cut off. The membrane (a) extends under (b),
        but not under the circular patches of membrane, (c, c.)

  4. Anelasma squalicola. Mandibles, seen from the side towards
        the maxillæ.

  5. Anelasma squalicola. Mandibles, seen from the side towards
        the labrum.

  6. Anelasma squalicola. The right-hand, rudimentary cirrus, the
        third from the mouth.

  7. Anelasma squalicola. Maxillæ. The thin horny apodeme, (a).

  8. Ibla Cumingii, female, (magnified four times.)

  8a´. Ibla Cumingii, female, (magnified about five times), with
        the right hand valves and right side of the peduncle
        removed. The Male (h) is seen attached in the sack. The
        peculiar form of the body, caused by the small development
        of the prosoma, by the distance of the first and second
        pairs of cirri, and by the distance of the mouth from the
        adductor muscle, (a dark dotted circle opposite i,) and
        lastly, the remarkable course of the oesophagus over the
        adductor muscle, together with the outline of the stomach,
        are here all exhibited.

        (a.) Scutum; the end of the large rounded adductor
          muscle, which was attached to the valve now removed,
          near its apex, is plainly seen.

        (b.) Tergum.

        (c.) On a line with this letter, is seen the largely
          bullate labrum, forming a blunt overhanging projection.

        (d.) Palpus, close to the upper segment of the pedicel of
          first cirrus.

        (e.) Orifice of the acoustic (?) sack, between the bases
          of the first and second cirrus.

        (f.) Caudal appendages.

        (g.) Branching ovarian tubes within the peduncle.

        (h.) Male, on the same scale, lying in its natural
          position within the sack, with the lower part of its
          peduncle bent upwards, and imbedded in the corium and
          muscles of the female.

        (i.) Adductor scutorum muscle.

  8b´. Ibla Cumingii, Internal view of the scutum and tergum,
        and of the upper part of the outer integument of the
        peduncle, with its horny spines magnified about three
        times.

  8c´. Ibla Cumingii, A small portion of the outer integument of
        the peduncle, greatly magnified, showing the horny
        persistent spines; two of the spines have been torn out.

  9. Ibla quadrivalvis; internal view of scutum and tergum, and of
        the upper part of the outer integument of the peduncle;
        magnified four times.

  9a´. Ibla quadrivalvis, Penis supported on a long
        unarticulated projection; greatly magnified.


TAB. V.

Fig.

  1. Male of Ibla Cumingii, magnified thirty-two times.

        (a.) Mouth.

        (b.) A slight double fold, formed by the basal edge of the
          labrum, and by a lower fold, which at (h) becomes well
          developed; the latter is a rudimentary representation of
          the double membrane and valves forming the capitulum.

        (c.) Eye.

        (d, d.) Torn membrane from the sack of the female,
          constricted round the body of the male.

        (e.) Terminal or basal point, with the prehensile larval
          antennæ, represented on rather too large a scale.

        (f.) The imbedded portion of the male.

        (g.) Two pairs of cirri.

        (h.) The fold above alluded to, concealing a small portion
          of the slightly retracted thorax.

  2. The male of Ibla Cumingii, viewed from vertically above;
        magnified about sixty times. The dotted lower portion,
        represents the outline of the thorax and the positions of
        the cirri, which, from standing below the mouth, could not
        be well seen, when the summit of the mouth was in the
        proper focus.

        (a.) Labrum, largely bullate.

        (b.) Palpi.

        (c.) Mandibles.

        (d.) Maxillæ.

        (e.) Outer maxillæ; between which and the crest of the
          labrum, the orifice of the oesophagus can be obscurely
          seen.

        (f.) Anus.

        (g.) Rudimentary caudal appendages, under which is the
          pore leading from the vesiculæ seminales.

        (h.) Posterior cirrus. (i.) Anterior cirrus.

  3. Male of Ibla Cumingii; labrum and palpi, as seen with the
        eye on a level with the summit of the mouth.

  4. Male of Ibla Cumingii, Posterior cirrus (h in fig. 2) much
        magnified.

  5. Male of Ibla Cumingii, Larval antennæ; from the terminal
        point of the body (e in fig. 1), as seen with a 1/8th of
        an inch object glass.

  6. Male of Ibla Cumingii, Outer maxillæ.

  7. Male of Ibla Cumingii, Mandibles, with the underlying
        articulated membrane, forming the side of the mouth.

  8. Male of Ibla Cumingii, Maxillæ, with the apodeme.

  9. Complemental Male of Scalpellum vulgare, attached over the
        fold in the occludent margin of the scutum of the
        hermaphrodite.

        (a.) Orifice of the sack of the male.

        (b.) Spinose projections above the rudimental valves; at
          the bottom of the figure are represented, as seen through
          the whole thickness of the animal, the prehensile larval
          antennæ.

        (d.) The depression for the attachment of the adductor
          scutorum muscle of the hermaphrodite; see fig. 15 a´.

        (e, e.) A transparent layer of chitine, which forms a
          border to the occludent margin of the scutum of the
          hermaphrodite. This border supports long spines, which are
          connected with the underlying corium by sinuous tubuli.

  10. The basal (normally anterior) portion of the above
        complemental Male, greatly magnified, viewed dorsally from
        above, exhibiting the larval prehensile antennæ, attached
        to the antero-sternal surface of the animal.

  11. One of the antennæ of ditto, viewed laterally and on the
        outside.

  12. Ditto, ultimate segment of.

  13. Body of the above complemental male, consisting of the thorax
        supporting the four pairs of limbs, and of the terminal
        abdominal lobe.

  14. Small portion of the outer integument of the complemental
        male, as seen with a 1/8th of an inch object glass.

  15. Scalpellum vulgare (hermaphrodite), magnified three times.

        (a, a.) Complemental males.

        (b.) Rostrum, of which a separate enlarged figure (b´)
          is given.

  15a´. Scutum of the hermaphrodite Scalpellum vulgare,
        internal view of.

        (a.) Fold on the occludent margin.

        (d.) Pit for the adductor muscle.


TAB. VI.

Fig.

  1. Scalpellum ornatum, (female, magnified seven times.)

  1a´. Scalpellum ornatum, Upper latus, viewed internally.

  1b´. Scalpellum ornatum, Scutum of full-grown specimen, viewed
        internally, much magnified.

        (a.) Depression for the adductor muscle.

        (b.) Depression for the reception of the male.

  1c´. Scalpellum ornatum, cutum of half-grown specimen, viewed
        internally, much magnified, on same scale with fig. 1 b´.
        The depression (b) for the reception of the male is here
        seen, in almost the first stage of formation.

  1d´. Scalpellum ornatum. An imaginary section through the
        cavity (x) in which the male is lodged.

        (a.) Section of the shell of the scutum of the female.

        (b.) A layer of chitine homologous with the shell, and
          partially lining the scutum.

        (c.) The inner lining (of chitine) of the sack of the
          female.

        (d.) A double fold of corium.

  2. Scalpellum rutilum, (magnified two and a half times).

  2a´. Scalpellum rutilum, Internal view of scutum, enlarged.

        (a.) Depression for the adductor muscle.

        (b.) Cavity for the reception of the male.

  2b´. Scalpellum rutilum, External view of carina.

  2c´. Scalpellum rutilum, Section across middle of carina.

  3. Complemental Male of Scalpellum Peronii, greatly magnified.

  4. Complemental Male of Scalpellum villosum, greatly magnified.

        (a´.) Natural size.

  4, a, b, c. Ditto, valves separated.

        (a.) Scutum.

        (b.) Tergum.

        (c.) Carina.

  5. Complemental Male of Scalpellum rostratum, a restored
        figure, greatly magnified. Scutum and rudimentary carina
        correct.

  6. Scalpellum Peronii, one and a half the natural size.

        (a.) Rostrum a little more enlarged, front view of.

  7. Scalpellum rostratum, magnified six times.

        (a.) Rostrum, front view of.

  8. Scalpellum villosum, magnified one and a half the natural
        size.

  8a, b. Scalpellum villosum

        (a.) Internal view of rostrum.

        (b.) Internal view of sub-rostrum.


TAB. VII.

Fig.

  1. Pollicipes cornucopia, (one and a half nat. size.)

  1a. Pollicipes cornucopia, internal view of valves.

  2. Pollicipes polymerus, (one and a half nat. size.)

  2a. Pollicipes polymerus, internal view of valves.

  3. Pollicipes mitella, nat. size.

  3a´. Pollicipes mitella, nat. size, internal views of

        (a.) Scutum, and of

        (b.) Tergum, showing articular fold.

  3b´. Pollicipes mitella, Internal view of other valves, in a
        small specimen, showing the manner in which the valves of
        the lower whorl overlap each other.

        (a.) Upper latera.

        (b.) Carina,

        (c.) Sub-carina, both viewed a little obliquely.

        (d.) Rostrum,

        (e.) Sub-rostrum, both viewed a little obliquely.

  4. Pollicipes spinosus, one and a half nat. size.

  5. Pollicipes sertus, one and a half nat. size.


TAB. VIII.

Fig.

  1. A piece of rock bored in two directions by Lithotrya
        dorsalis, with the calcareous basal discs in the upper
        cavity, serving as a bridge for crossing an old cavity.
        About twice natural size.

  1a´. Lithotrya dorsalis, (nearly twice nat. size), with the
        basal calcareous cup adherent; (a), rostrum on same scale,
        seen externally.

  1b´. Lithotrya dorsalis, rostrum and the rostral corners of
        the two scuta, together with a small portion of the
        subjacent membrane of the peduncle, with its calcareous
        scales; viewed externally, greatly magnified, showing the
        inferior crenated edges of the scales.

  1c´. Lithotrya dorsalis, basal calcareous cup, one and a half
        the natural size; this is the largest specimen which I have
        seen.

  2. Lithotrya Nicobarica, (magnified nearly twice;) attached to
        the rock, copied from Reinhardt; (a), rostrum on the same
        scale, with the other valves, seen externally; (b),
        section of the row of discs; (c), extreme point of the
        peduncle, extending beneath the row of discs.

  2a´. Rock bored by Lithotrya Nicobarica, showing the row of
        calcareous discs, copied from Reinhardt.

  3. Lithotrya cauta, magnified between seven and eight times;
        (a), scutum; (b), tergum.

  3c. Lithotrya cauta, latus, greatly magnified.

  3d. Lithotrya cauta, uppermost scales of the peduncle, greatly
        magnified.

  3e. Lithotrya cauta, star-shaped discs of hard chitine,
        supported on a peduncle of the same substance, taken from
        the lower exterior surface of the peduncle, very greatly
        magnified.

  4. Lithotrya Rhodiopus, (magnified five times,) internal views
        of; (a), scutum; (b), tergum; (c), latus; (d),
        carina.

  5. Lithotrya Valentiana, (magnified between three and four
        times;) (a), internal view of scutum and tergum, locked
        together; (b), capitulum seen from vertically above;
        (c), internal view of carina; (d), section across the
        middle of the carina.


TAB. IX.

Fig.

  1. Lithotrya truncata, (magnified four times.)

  1a´. Lithotrya truncata, capitulum seen from vertically above,
        not so distinctly represented as in fig. 5 b, Pl. VIII.

  1b´. Lithotrya truncata, internal views of valves; (a),
        rostrum, with a few subjacent scales of the peduncle; (b),
        scutum; (c), tergum; (d), carina.

  2. A portion (about 1/10th of an inch square) of the surface of
        attachment of the peduncle of Pollicipes polymerus, seen
        from the outside, greatly magnified, showing the small
        circular (bb) patches of cement, poured out from the
        cement-ducts (aa) which lie within the peduncle.

  2a´. A portion of a section, still more magnified, through the
        basal membrane of the peduncle, through one of the loops of
        the cement-ducts (aa), and through one of the circular
        patches (b) of cement.

  3. Cement gland, duct, and ovarian tubes of Conchoderma aurita;
        (aa), ovarian tubes, with ova in process of formation;
        (b), cement-gland; (c), cement-duct.

  4. Conchoderma virgata, enlarged, with one side of the capitulum
        and of the peduncle removed, to show the form and position
        of the body.

        (a.) tergum, edge of.

        (b.) mouth, with one of the palpi seen on the inner, upper
          corner.

        (c.) adductor scutorum muscle.

        (d.) orifice of acoustic (?) sack.

        (e.) scutum, occludent margin of.

        (f.) branching ovarian tubes within the peduncle.

        (g.) filamentary appendage on the prosoma.

        (h.) ditto, close to basal articulation of the first
          cirrus.

        (i.) ditto, on the pedicel of the first cirrus.

        (j.) ditto, on the pedicel of the third cirrus.

        (k.) ditto, on the pedicel of the fourth cirrus.

        (l.) ditto, on the pedicel of the fifth cirrus.

        (m.) edge of the carina.

        (n.) prosoma.

  5. Apex of one of the filamentary appendages of Conchoderma
        aurita, greatly magnified, exhibiting the included
        branching testes.

  6. Acoustic (?) sack of Conchoderma virgata, taken out of the
        acoustic meatus, with the diaphragm from the summit removed;
        greatly magnified.

  7. Terminal part (magnified seven times), of the peduncle of an
        elongated specimen of Scalpellum vulgare, slit open, with
        the corium removed, showing the two cement-ducts (aa), and
        a row of circular patches (bb) of cement, by which the
        peduncle, along its rostral edge, is attached to the thin
        horny branches of the coralline. The larval antennæ are seen
        at the terminal point, and the two cement-ducts can be
        traced into them.


TAB. X.

Figures all greatly magnified.

Fig.

  1. Mandibles of Pollicipes mitella: exhibiting the upper (a)
        and lower (b) articulations, and the three principal
        muscles; the short upper cut off muscle runs to its
        attachment at the base of the palpus.

  2. Mandibles of Lithotrya dorsalis, exhibiting four (aa)
        roughened, thin, ligamentous apodemes for the attachment of
        the muscles.

  3. Mandibles of Scalpellum Peronii.

  4. Mandibles of Ibla Cumingii.

  5. Mandibles of Lepas anatifera.

  6. Palpus of Lepas anatifera.

  7. Palpus of Pollicipes mitella.

  8. Palpus of Alepas cornuta.

  9. Maxilla of Lepas anatifera.

  10. Maxilla of Lithotrya dorsalis, exhibiting the horny, rigid
        apodeme (a) buried in muscles, together with the two other
        principal bundles of muscles.

  11. Maxilla of Ibla Cumingii.

  12. Maxilla of Lithotrya Rhodiopus.

  13. Maxilla of Pollicipes polymerus.

  14. Maxilla of Pollicipes mitella.

  15. Maxilla of Poecilasma eburnea.

  16. Outer maxilla of Conchoderma virgata; (a), orifice of the
        olfactory cavity, the inner delicate chitine membrane of
        which is seen within, the specimen having been treated with
        caustic potash.

  17. Outer maxilla of Pollicipes mitella, showing the two
        principal muscles, and the prominent, tubular, (b)
        olfactory orifices.

  18. Caudal appendages, and basal segments of the sixth pair of
        cirri, of Lepas anatifera; (a), anus; (b), caudal
        appendages; (c), lower segment of pedicel of sixth cirrus;
        (d), upper segment of ditto; (e), basal segments of the
        two rami.

  19. Caudal appendage (right-hand side) of Pollicipes sertus.

  20. Caudal appendage (right-hand side) of Scalpellum Peronii.

  21. Caudal appendage (right-hand side) of Scalpellum vulgare.

  22. Caudal appendage (right-hand side) of Pollicipes cornucopia.

  23. Caudal appendage (left-hand) Lithotrya dorsalis; (a),
        caudal appendage; (c), lower segment of pedicel of sixth
        cirrus; (d), upper segment of ditto; (e), segments of
        one of the rami.

  24. Portion of caudal appendage of Lithotrya dorsalis, highly
        magnified.

  25. Pollicipes polymerus; anterior ramus of the second cirrus.

  26. Lepas anatifera; a segment of the sixth cirrus, showing the
        arrangement of the spines; (a), main anterior spines, of
        which there is a corresponding row on the opposite side;
        (c), dorsal tuft.

  27. Pollicipes polymerus; a segment of the sixth cirrus, showing
        the arrangement of the spines; (a), main anterior spines,
        of which there is a corresponding row on the opposite side;
        (b b), calcareous shields on the dorsal surfaces, with
        tufts of fine spines near their upper edges.

  28. Alepas cornuta; sixth cirrus of; (a) basal portion of one
        ramus, consisting of numerous segments; (k), the other and
        almost rudimentary ramus.

  29. Poecilasma fissa; segments of the sixth cirrus, showing the
        arrangement of the spines; (a), anterior spines; (c),
        dorsal tufts.

[THE END]
Charles Darwin's Book: Monograph on the Sub-class Cirripedia, Volume 1

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