Class—CRUSTACEA. Sub-Class—CIRRIPEDIA. (continued 7)

Terga, projecting beyond the other valves to an unusually small degree, broadly oval; basal angle bluntly pointed, apex rounded, blunt; scutal margin, hollowed out to receive the upper part of the tergal margin of the scuta; carinal margin curved and protuberant; occludent margin consists of two short sides at right angles to each other. The whole valve in length and area is about equal to the scuta; internally, somewhat concave.

Carina, triangular, rather narrow, internally deeply concave, very slightly curled inwards; basal margin protuberant, with a large central portion considerably hollowed out.

Rostrum, triangular, of nearly the same shape as the carina, but only one third of its length, internally very slightly concave, and with the basal margin various, being either truncated or angularly prominent in the middle.

Latera.—The upper pair (corresponding to the interval between the scuta and terga) is only a trifle larger than the latera immediately beneath; and these only a little larger than those lower down. In the lowest whorl, the valves are very minute, though still about twice as large as the scales on the peduncle, and of a different shape from them. The upper latera (viewed internally) are almost diamond-shaped, owing to the prominence of the basal margin, but this varies considerably in degree. The latera in the next whorl are triangular, with the basal margins protuberant and arched, in a less and less degree in the lower whorls, until in the lowest, the valves are elongated transversely.

Microscopical Structure.—A valve placed in acid leaves a thick opaque mass, formed of three different kinds of tissue, one having a finely shaded appearance; a second with a largely hexagonal reticulated structure, and the third thin, transparent, and marked with arborescent lines, which I imagine to be tubes, as will be hereafter seen in Lithotrya. Near the exterior surface, there are many tubuli. It appears to me probable that the strong tendency which the valves in this species have to disintegrate, is connected with the unusual quantity of animalized tissue contained by them. Externally the valves are covered by a strong membrane, either white or yellow, or white streaked with yellow, and marked by lines of growth, and by longitudinal, sinuous, little ridges.

Peduncle, in the upper part, of rather less diameter than the capitulum; twice or thrice as long as it; tapering a little downwards; surface of attachment wide and flat. Calcareous scales, minute, symmetrically and closely packed together: each scale is much flattened, and its shape, including the imbedded portion, is that of a spear with its point broken off. The basal end of each scale is conically hollow, and from the layers of growth conforming to this hollow, there is a false appearance of an open tube running through the scale.

Attachment.—The surface of attachment is wide: the two cement-ducts, after running down the sides of the peduncle in a sinuous course, within the longitudinal muscles and close outside the ovarian tubes, pass through the corium, and then separately form the most abrupt loops or folds. These are represented in Pl. IX, fig. 2, in which a space about 1/10th of an inch square is given, as seen from the outside. At each of the bends, an aperture has been formed through the membrane of the peduncle, and cement poured forth. The manner in which the discs of cement (b) come out of the two ducts (a a), and reach the external surface, is shown in the section, figure 2 a´. The two tubes are firmly attached to the older layers of membrane, and are covered by the last-formed layers. In a young specimen, the cement-ducts were a little above 2/2000ths of an inch in diameter, which had increased, in a medium-sized specimen, to 5/2000. The cement-glands are retort-shaped, seated near each other, high up in the peduncle.

Size.—The largest specimen which I have seen, was three inches in length including the peduncle; the capitulum was 9/10ths of an inch long, and one in width.

Young Specimen.—I examined one with a capitulum 18/1000ths of an inch long, measured from the lowest whorl to the tips of the terga; the width was only 13/1000ths of an inch; in old specimens the width of the capitulum is greater than the length. The length of one of the scuta was 14/1000ths of an inch, therefore, greater than the width of the entire capitulum, which is not the case with mature specimens. Besides the scuta and terga, the carina and rostrum, and three pair of large latera, there was a lower whorl formed of ten or twelve valves, giving altogether to the capitulum of this very small specimen, either twenty-two or twenty-four valves.

Shape of Body, Sack, Colours, &c.—From the position of the orifice of the capitulum, the animal’s body is suspended to the scuta in a more transverse direction than is usual. The prosoma is well-developed, and is distinctly separated from the three posterior thoracic segments, by a band of thin membrane. The tunic of the basal part of the sack, where it enters the peduncle in a blunt point, is thickened and covered with roughened rounded papillæ. The corium of the sack under the valves, is coloured (after spirits) so dark a brown as to be nearly black; the cirri and trophi are similar, but with a tinge of greenish-purple.

Filamentary Appendages.—Of these there were, on the prosoma of one specimen, twelve pairs, and in another specimen fourteen pairs, seated in two approximate rows; the middle filaments are the longest, equalling about half the diameter of the thorax: each is flattened, and tapers but little towards its summit, which is roughened with microscopical crests serrated on both sides; on the summit, also, there are a few bristles and some very short, thick, minute spines. These appendages are directed rather towards each other, and towards the thorax. I do not doubt that their numbers vary according to the size of the specimen. I believe that they are occupied by testes. Outside these filaments, on each side of the prosoma, there are two very irregular rows of papillæ, intermediate in length between the filaments and the rounded swellings at the bottom of the sack. Beneath the basal articulation of the first cirrus, there is on each side, a short appendage, with a few bristles on its summit. Lastly, on each side of the middle of the mouth, on the prosoma, there is a longer appendage, dark-coloured, furnished with a few scattered bristles on its sides and apex, and directed upwards and a little towards the adductor scutorum muscle.

Mouth.—Labrum highly bullate, but with the uppermost part not more bullate than the lower part, and therefore not overhanging it; basal margin much produced; crest with some small blunt teeth and some bristles. The inner fold of the labrum is much thickened, yellow, punctured, and with a tuft of fine bristles on each side.

Palpi, approaching each other but not touching, club-shaped, or with broad and square extremities, thickly fringed with serrated bristles.

Mandibles with three unusually strong teeth, slightly graduated in size, with the inferior angle very coarsely pectinated; the lower edges of the main teeth are roughened.

Maxillæ, (Pl. X. fig. 13). Spinose edge about half the length of the mandibles; the two upper spines are unusually strong; close under, and almost hidden by them, there is a tuft of fine spines; in the middle there is a second similar tuft mounted on a prominence; and at the inferior angle there is a third tuft, also mounted on a rather wider prominence, not quite accurately figured. In the interspaces between these tufts there are three or four pairs of spines of the usual appearance and projecting just beyond the fine tufts; the upper of the two interspaces is rather narrower, but rather deeper, than the lower interspace. Apodeme very long, irregularly shaped, like an S, with a remarkable elbow near its attachment; apex slightly enlarged, thin and rounded.

Outer Maxillæ.—On the inner margin there is a deep and conspicuous notch, above and beneath which, there is a compact row of serrated bristles; exteriorly the bristles are rather longer.

Olfactory Orifices very prominent, pointing obliquely towards each other.

Cirri.—Posterior cirri moderately long, much curled, with the segments (Pl. X, fig. 27) flattened and wide; the anterior surface hemispherically protuberant, supporting six pairs of spines, of which the lower ones approach each other; between these spines there is a large tuft of very fine spines, of which the central ones are the longest; there is an upper lateral group of very short strong spines; dorsal tufts composed of short, fine numerous spines. First pair seated close to the second pair, short, having in both rami eight segments, whereas in the same individual the second pair, which is nearly twice as long, had thirteen, and the sixth pair eighteen segments. Rami of the first pair nearly equal in length, with their segments, excepting the two upper ones, thickly paved with bristles, in the midst of which a tuft of fine spines, as in the posterior cirri, may be distinguished; the dorsal tufts encircle the whole of each segment; the spine-bearing anterior surfaces are protuberant chiefly in the upper part, so that they are oblique. The posterior (?) ramus has its segments much wider than those on the other ramus; and amongst the common spines, in the third and fourth segments, (counting from the bottom,) there are some very strong spines with their upper ends coarsely and doubly pectinated, each tooth being upwardly bent into a rectangular elbow. In the fifth segment, some of the spines are doubly pectinated with simple teeth; and most of the spines are doubly serrated. The Second (Pl. X, fig. 25) and Third cirri have the five basal segments (5/13ths of the whole number in the second cirrus, and 5/14ths in the third cirrus) of their anterior rami, extremely broad, protuberant, and paved with serrated bristles, amongst which, (except on the actual lowest segment,) there are some simply pectinated spines, and others with their teeth elbowed, exactly as in the first cirrus. The basal segments of the posterior rami of the second and third cirri, differ from the three posterior cirri only in the spines being slightly more numerous; but none of them are pectinated.

Pedicels, rather short; the upper segment resembles, in the arrangement of its spines, the segments of the posterior cirri; the lower segment is longer than the upper, and has two tufts of fine spines, between the two rows of long spines. In the second and third cirri, these two intermediate tufts on the lower segment of the pedicel, are not so distinctly separated from each other.

Caudal Appendages, very small, uniarticulate, blunt and rounded; tips bearing a few, very short, thick spines.

Alimentary Canal.—Œsophagus, somewhat curved at the lower end, where it enters the stomach, which has no cæca; rectum, unusually short, extending from the anus only to the base of the fifth pair of cirri. Within the stomach, from top to bottom, there were thousands of a bivalve entomostracous crustacean.

Generative System.—Both ovaria and testes are largely developed; the former fill the long peduncle; the testes enter both the pedicels of the cirri, and the filamentary appendages on the prosoma; vesiculæ seminales very large, reflected at their ends, extending across each side of the stomach. Penis rather small, coloured purplish, with numerous little tufts of bristles.

Variation.—In some specimens in the British Museum, collected by Sir J. Ross, in the Southern ocean, and in another older set from an unknown source, several parts of the outer tunic of the animal’s body presented the remarkable fact of being calcified, but to a variable degree; whereas in several specimens from California, there was no vestige of this encasement. Considering it most improbable that the calcification of the integuments should be a variable character, I most carefully compared the above-mentioned sets of specimens, valve by valve, trophi by trophi, and cirri by cirri, and found no other difference of any kind; therefore I cannot hesitate to consider both to be the same species. The first Southern specimen which I examined presented the following characters: on the prosoma there was a central longitudinal band, formed of a thin, brittle, brown-coloured calcified layer, which became irregularly rather narrow towards the thorax; on each side it sent out six or seven irregular rectangular plates, which surrounded and supported the bases of the two rows of filamentary appendages; and outside these, some of the papilliform projections also had their bases surrounded by small, calcified, separate rings. The thoracic segments corresponding with the second, fourth, fifth, and sixth cirri had, on each side, an elongated calcified plate; on the ventral surface of the thorax, between the first and second cirri, there were two minute plates. In all the cirri, excepting the first pair, the segments of the rami, and in the three posterior pairs, the segments of the pedicels, had their dorsal surfaces strengthened by oblong, quadrilateral, calcified shields, the upper margins of which are notched for the dorsal tufts of spine, and the two lateral margins are also slightly hollowed out; these are represented in figure 27. The lower segments of the pedicels of some of the cirri, had an additional calcified plate on the antero-lateral face.

These plates are of a faint-brown or yellowish colour, and are conspicuous: the degree of calcification differs considerably; some are quite brittle and very thin, others half horny, and effervesce only slightly in acids. After having been placed in acid, there is no apparent difference between the parts before occupied by the calcified plates and the surrounding membrane; these plates, however, are not superficial, but consist of several of the laminæ, which together compose the ordinary integument, in a calcified condition. Like the integuments of the body, and unlike the valves of the capitulum, these calcified plates are thrown off at each exuviation. Neither the exact shape nor number of the plates corresponded in different individuals, nor even on opposite sides of the same individual. The margins of the plates often have a sinuous corroded appearance; they are, moreover, often penetrated by minute rounded holes, that is, by minute, rounded, non-calcified portions. In one specimen from the Antarctic expedition, there were only here and there a single shield on the segments of the posterior rami, and no plate on the prosoma. Of two specimens in another and older set in the British Museum, from an unknown locality, both had shields on the segments of the cirri, but only one had the large plate on the prosoma. I may here mention that in one specimen, in which the calcified plates were most developed, and which was nearly ready to moult, there were, within the filamentary appendages on the prosoma, small irregular balls of calcareous matter, appearing to me as if calcareous matter had been morbidly excreted, and not like a provision for the future.

Range.—This species, in the present state of our knowledge, seems to range further than any other of the genus, extending from Upper California, (lat. 32° to 35° N.,) across the Pacific, to at least 32° S., perhaps much farther south, for it was collected during the Antarctic expedition, and 32° was the highest latitude traversed by that expedition.

Affinities.—This species is closely related to P. cornucopia and P. elegans, but differs rather more from them, than these two do from each other. In the capitulum the chief distinctive characters are—the more perfect graduation in size, and the greater number, (taking equal-sized specimens,) of the whorls of latera—the darker colours—the central part of the basal margin of the carina in this species, being considerably excised—the peculiar form of the basal margin of the scuta—and lastly, the scutal margin of the terga being more hollowed out. In the animal’s body, the most obvious distinctive character is the uniarticulate caudal appendage. This species agrees with P. elegans, in the presence of the singular elbowed teeth, on some of the spines in the first three pairs of cirri.

4. Pollicipes mitella. Pl. VII, fig. 3.

Lepas mitella. Linn. Systema Naturæ, 1767.

Pollicipes mitella. G. B. Sowerby. Genera of Shells, fig. 2.

Polylepas mitella. De Blainville. Dict. Sc. Nat. (1824) Plate, fig. 5.

Capitulum Mitella. J. E. Gray. Annals of Philosoph., new series, vol. x, 1825.

P. capitulo valvarum unico sub-rostro verticillo instructo: laterum pari superiore (introrsum spectanti) inferiorum magnitudinem ter aut quater superante: lateribus inferioribus utrinque obtegentibus: pedunculi squarmarum verticillis densis, symmetricè dispositis.

Capitulum with only one whorl of valves under the rostrum: the upper pair of latera, viewed internally, are three or four times as large as the lower latera, which overlap each other laterally: scales of the peduncle symmetrically arranged in close whorls.

Maxillæ, deeply notched: caudal appendages, multi-articulated: filamentary appendages, none.

Philippine Archipelago, Mus. Cuming: China Sea, Mus. Brit.: Amboyna and East Indian Archipelago, according to Rumphius and other authors: Madagascar, according to J. E. Gray.

Capitulum, compressed, consisting of the scuta, terga, carina, rostrum, and a large pair of upper latera, with a single lower whorl of smaller valves; these latter vary from 22 in very small specimens, to 26 in large specimens. The capitulum, therefore, is formed of at most 34 valves; but in the largest specimen seen by me, the capitulum being 2.3 of an inch in width, there were only 32 valves. In the smallest, namely, with a capitulum .15 of an inch in width, there were 30 valves. The valves are remarkably strong, and formed of white shelly matter; they are closely approximate, and overlap each other: the scuta and terga are articulated together by a fold; the apices of the valves are either worn and disintegrated, or they project freely like horns beyond the sack, to a much greater extent than in any other recent species of the genus: even a considerable portion of the scuta projects obliquely upwards. The exterior surfaces of the valves (when not worn) are covered by a strong yellow membrane, and the upper free parts are generally attached together for some little length by this same membrane. The valves are plainly marked by the zones of successive growth; and most of them are ribbed and furrowed slightly, from their umbones to their basal margins. The yellow external membrane, examined microscopically, is marked by, or rather formed of, numerous growth-lines, crossed by longitudinal beaded ridges. The tubuli are not numerous, and of small diameter.

Scuta (Pl. VII, fig. 3 a´, a) triangular, with the apex more or less produced, according to the state of its preservation, and a little curved towards the terga; basal margin, and in some degree the tergo-lateral margin, arched, and slightly protuberant; occludent margin thickened, slightly prominent, with the inner edge covered by the yellow membrane, like the exterior surface of the valve. The upper part of the tergo-lateral margin overlaps a little the edge of the tergum, and receives it in a furrow,—the two valves being thus locked together. This furrow lies in the freely-projecting, membrane-covered portion, and extends up to the apex; it is of variable depth. Internally the scuta are concave, and in some old specimens to a high degree. In these latter, the basal margin, towards the tergo-lateral side, is strongly sinuous; the prominences are formed by the terminations of the external longitudinal ridges, and correspond to the interspaces between the valves of the lower whorl. These ridges, which are interesting, from throwing light on similar ridges in some fossil species, are present, both on old and young specimens, and run from the apex of the valve, in a slightly curved line, to the tergo-lateral half of the basal margin, where, as we have just seen, they sometimes form prominences. They consist of three or even four obscure, almost confluent, ridges, of which the middle one is generally (but not always) the smallest: together they cover the whole of that part of the scutum, which is not overlapped along the basal margin by the rostrum and large upper latus; and they seem evidently due to the growth of the shell in this interspace having been freer. So, again, the three or four small, confluent, component ridges have the same relation to the interspaces between the small latera of the lower whorl.

Terga large, four-sided, with the internal growing surface (fig. 3 a´ b), almost diamond-shaped; basal angle blunt, rounded; exteriorly, from the apex to the basal angle there is a rather broad, very slight prominence, which bears the same relation to the carina and upper latus, as do the compound ridges on the scuta to the rostrum and upper latus. The upper part of the scutal margin forms a slightly-projecting, rounded shoulder, though variable in its degree of prominence, in relation to the variable depth of the recipient furrow in the scuta. Externally, parallel to the occludent margin, and close below the prominent shoulder, just mentioned, there is a slight and variable depression, extending up to the apex of the valve. This depression is due to the prominence, variable in degree, of the tergal edge of the recipient furrow in the scuta.

Carina, triangular, strong, inwardly bowed, generally with a large upper portion freely projecting; exteriorly with a narrow, sharp, central ridge or keel, which is solid, the interior concavity not reaching so deep; inner growing surface (fig. 3 b´, b) deeply concave, triangular. Basal margin square—that is, transverse to the longer axis of the carina, or it even rises (as is best seen in the growth-ridges) a little towards the exterior keel. On each side of the central exterior keel, there is a narrow longitudinal ridge, corresponding with the interspace between the sub-carina and the next-but-one latus of the lower whorl; the latus next to the sub-carina is very small, and overlies the ridge itself. In a very large specimen, these lateral longitudinal ridges formed (as they likewise did on the rostrum) slight prominences on the basal margin. In one specimen the carina was straight.

Rostrum closely similar, in almost every respect, to the carina, even to the exterior, lateral, longitudinal ridges, and in their relation to the interspaces in the lower whorl. The valve is generally not so long, but rather wider, more inwardly bowed, and with the exterior solid keel less prominent than in the carina. The inner growing surface (fig. 3 b´ d) is less acuminated at its upper end.

Upper pair of Latera.—These are much larger than the remaining valves of the lower whorl; they are straight, triangular, and much acuminated, with their apices, when well preserved, extending far up, for fully three fourths of the height of the scuta. They nearly equal in length the carina. The growing surface (fig. 3 b´, a) is flat, triangular, in well-preserved specimens forming only a third or a quarter of the entire length of the valve. In the middle of the basal margin there is a very slight prominence, corresponding with a slight external central ridge, formed as heretofore by the overlapping of two of the valves of the lower whorl. Basal margin nearly on a level with that of the scuta and with the basal points of the terga. The foregoing eight larger valves form the main cavity, in which the body of the animal is lodged.

Valves of the Lower Whorl.—These, seen externally, seem to belong to more than one whorl, but internally their basal margins stand on a level. They vary in number, as already stated, from 22 to 26. I have seen an individual with a valve more on one side than on the other. They are of unequal sizes, but they are rather variable in this respect: the largest are not above half the size of the upper latera: three or four pairs, together with the sub-rostrum (e) and sub-carina (c), are always larger than the others: these two latter valves differ from the others only in being more concave. Seen externally, all these valves project considerably, and curl a little inwards, with their apices generally worn and truncated. Viewed internally (fig. 3 b´), whilst the valves are in their proper places, the inner and growing surfaces of the smallest are seen to be triangular,—of the larger, some are rhomboidal, and others quadrilateral with the upper side much longer than the lower. These latter valves overlap the upper parts of the little valves on both sides of them; the rhomboidal valves overlap a valve on one side, and are overlapped on the other; the triangular valves are overlapped on both sides.

The corium lining the capitulum is produced into narrow purple crests, which enter the interstices between the valves, more especially along the line separating the upper and lower whorls. There is, also, a distinct flattened, tapering, free projection of corium, which enters between the carina and sub-carina; and another between the rostrum and sub-rostrum.

Peduncle, much compressed, short, rarely as long as the capitulum; in one very large specimen it was extremely short, barely one fifth of the length of the capitulum. The attached portion, which is moderately pointed in young specimens, becomes extremely broad in old specimens. The calcified scales sometimes differ a little in size, in specimens of the same age: they are always compactly and symmetrically arranged: in old specimens they are much larger than in young ones: each scale has, at first, a transversely elliptic growing base, which ultimately becomes nearly circular. Exteriorly the tips of the scales are always disintegrated; they are sometimes club-shaped, owing to the scales having been re-added to after a period of reduced growth. The scales are fringed with brown disintegrating membrane.

Attachment.—At the base of the peduncle, the two cement-ducts running together, twist about in a singular manner, and at their bends pour forth cement. According to the age of the specimen, the ducts vary in diameter from 1/2000th to 5/2000ths of an inch. The two cement glands are small and difficult to find; they are retort-shaped, with two ovarian tubes entering each. They lie close together, in nearly the centre of the peduncle, and less than half-way down it. This proximity of the two cement-glands, and their position low down the peduncle, are of interest in relation to the position of these same glands in the sessile Cirripedes.

Size and Colours.—This is the largest and most massive species in the family. I have seen one specimen in the British Museum, from the Coast of China, 2.3 inches across the capitulum, and 1.5 in length, with the valves surprisingly thick. The relative width and length of the capitulum varies. The sack (in specimens long kept in spirits) is dirty purple, and exteriorly between the scuta, dark purple. The cirri, trophi, penis, caudal appendages, three posterior segments of the thorax, and the abdominal surface are dark-brownish purple.

Body.—Thorax remarkably compressed and carinated; prosoma pretty well developed. Extending from the base of the second cirrus, to nearly a central line on the thorax, there is on each side a rounded ridge: there is a second transverse ridge, running from the base of the first cirrus to near the adductor scutorum muscle: these ridges seem formed merely to allow of the larger development of the testes.

Mouth.—Labrum highly bullate; crest without any teeth, but with a few minute hairs. The inner fold of the labrum forming the supra-œsophageal cavity, is thickened, and shows a trace of a central line of junction, as in Sessile Cirripedes.

Palpi (Pl. X, fig. 7), small; of a singular club-like shape, owing to the convexity of the outer margin; exterior spines long, all doubly serrated.

Mandibles (Pl. X. fig. 1), with five teeth, of which the second is very small; inferior angle coarsely pectinated.

Maxillæ (fig. 14), with a deep narrow notch (bearing some fine spines) beneath the two upper great spines, which stand on a prominence; edge straight, bearing fourteen or fifteen pairs of spines: on the inferior angle there is an obscure tuft of shorter and finer spines: apodeme long, sinuous, and slender.

Outer Maxillæ (fig. 17), with the inner margin divided by a deep notch into two lobes, of which the upper one is rather short; both are clothed with a compact row of short bristles; exterior margin with longer bristles.

Olfactory Orifices, large and prominent to an unusual degree.

Cirri, moderately long and curled; the four posterior pair are alike; each segment has its anterior face somewhat protuberant, and bears six pairs of long spines, with a rather large, narrow tuft of intermediate spines, some of which are finely and doubly serrated. The dorsal tufts consist of short, thick spines, with some fine longer ones. The first cirrus is seated near the second; its rami are slightly unequal in length; lower segments paved with bristles; one ramus is thicker than the other, and some of its segments have coarsely pectinated spines. Second cirrus has the five basal segments of its anterior ramus highly protuberant, and paved with bristles, of which some are coarsely pectinated; the basal segments of the posterior ramus are rather more thickly clothed with bristles than are the posterior cirri, but otherwise resemble them. The third cirrus, as already stated, is exactly like the three posterior pairs; and this is a very unusual circumstance. On the dorsal surfaces and sides of the pedicels of the posterior cirri, there are some scattered, short, thick, minute spines.

Caudal Appendages, multi-articulate: in a medium-sized specimen, each contained eight segments, which reached half-way up the upper segment of the pedicel of the sixth cirrus. Lower segments flattened; the upper, tapering, and cylindrical; all have their upper margins furnished with stiff, little spines. In a young specimen (only .3 of an inch in length, including the peduncle), the caudal appendage contained only four segments, and the tip did not reach to the upper edge of the lower segment of the pedicel of the sixth cirrus.

Stomach, without cæca.

Generative System.—Vesiculæ seminales not reflexed at their broad ends; white, spotted with black. Testes, pear-shaped, borne on long footstalks: penis covered with minute bristles, in little tufts arranged in straight lines. The ovarian tubes fill up the peduncle to its base, but do not surround the sack; they are of small diameter, and simply branched. There is a very narrow ovigerous frænum, with a straight edge, lying on each side under the line of junction between the scutum and upper latus.

Affinities.—This species differs from all the others of the genus, in the third cirrus resembling exactly the three posterior pairs. In most of its characters—namely, in the symmetrical arrangement of the scales on the peduncle, in the considerable size of the valves of the lower whorl, in the general approximation of the valves, in the multi-articulated caudal appendages, in the form of the outer maxillæ, in the prominent olfactory orifices, in the basal segments of the anterior ramus alone of the second cirrus being paved with bristles, there is more affinity to P. cornucopia, P. elegans, and P. polymerus than to P. sertus and P. spinosus.

In the scuta and terga being articulated together, in the union of all the valves by stiff membrane, in the peculiar manner in which the valves of the lower whorl overlap each other, in the corium entering between some of the valves in filiformed appendages, in the near equality of size of the rostrum and carina, in the shortness of the peduncle in old specimens, in the position of the cement-glands, and lastly in the characters of the third pair of cirri, this species presents a closer affinity to the sessile Cirripedes, more especially to the Chthamalinæ, than does any other species of any other genus amongst the Lepadidæ. The movements, however, of the four opercular valves are not at all more independent of the other valves, than in the other Pedunculated Cirripedes; and the peduncle is furnished with all its characteristic muscles.

5. Pollicipes spinosus. Pl. VII, fig. 4.

Anatifa spinosa. Quoy et Gaimard. Voyage de l’Astrolabe. Pl. xciii, fig. 17.

P. capitulo valvarum uno aut pluribus sub-rostro verticillis instructo: laterum pari superiore vix inferioribus longiore: membranâ valvas tegente (post desiccationem) subfuscâ flavescente: pedunculi squamis inæqualibus, non symmetricis: verticillis longiusculè distantibus.

Capitulum with one or more whorls of valves under the rostrum: upper pair of latera only slightly larger than the lower latera: membrane covering the valves (when dried) light yellowish-brown: scales of the peduncle of unequal sizes, unsymmetrical, arranged in rather distant whorls.

Maxillæ, with the edge square and straight: caudal appendages uniarticulate: filamentary appendages, none.

New Zealand. Mus. Jardin des Plantes, Paris: Mus. Cuming.

Capitulum, flattened, triangular, broad, with the valves varying in number, in full-grown specimens of the same size, from 30 to above 60; the scuta, terga, and carina are very much larger than the other valves; the rostrum, however, is nearly half the size of the carina; the remaining valves are exceedingly small. In some specimens there is only one whorl under the carina; in other specimens there are distinctly two whorls. The scuta, terga, and carina stand pretty close together; they are moderately thick, and are covered, in chief part, by yellowish-brown membrane, which is destitute of spines.

Scuta, triangular, broad, basal margin slightly protuberant.

Terga, as large as the scuta, flat, regularly oval, basal point blunt and rounded.

Carina very slightly curved, triangular, internally rather deeply concave, basal margin straight. The inner and growing surface is four fifths of the entire length of the valve. In half-grown specimens the apex projects a little outwards.

Rostrum, small, much curled inwards; the basal margin is much hollowed out; the inner surface is broadly triangular, more than twice as wide as high, and about one fourth of the entire length of the valve. The remaining valves, about 26 in number, do not correspond on the opposite sides of the same individual, they are exceedingly small, with the sub-carina, sub-rostrum, and three pairs of latera a trifle larger than the lower latera, which are generally arranged in two whorls. In shape all the latera are nearly alike; they consist of flattened styles, with their inner surfaces transversely oval, and more or less elongated, the larger ones being most elongated.

Peduncle, broad, barely as long as the capitulum. The calcareous scales are irregularly shaped, minute, elongated and pointed, placed in separate transverse rows, and crowded together in each row. Only the scales in the uppermost row grow regularly; but some of the lower scales continue to be added to irregularly, and hence are the largest. On the other hand, the lower part of the peduncle, from the first formed scales having been worn away, is often quite naked. From this cause, and from the continued and irregular growth of some of the lower scales, the rows in this part of the peduncle, generally become irregular. The surface of attachment is broad.

In a half-grown specimen, with a capitulum only 3/10ths of an inch long, all the lower valves were considerably larger in proportion to the scuta, terga, and carina, than in full-grown individuals.

Size and Colours.—Length of capitulum in the largest specimen, 7/10ths of an inch; breadth, slightly exceeding the length. Colours after having been long in spirits—upper part of sack, thorax, pedicels of cirri, and penis, clouded with fine purple; cirri banded with the same; exterior convex surface of the outer and inner maxillæ and palpi dark purple; prosoma yellow. The membrane of the peduncle and of the capitulum is dirty yellow, with bands of purple between some of the valves.

Filamentary Appendages, none. Ovigerous fræna placed near the middle of the basal margin of the scuta; small, semi-oval, with an elliptical ring of bead-like glands; glands seated on long footstalks.

Mouth.—Labrum far produced towards the adductor muscle; upper part highly bullate, nearly equalling the longitudinal diameter of the rest of the mouth, and very slightly overhanging the lower part; crest with very minute bead-like teeth.

Palpi, with their inner margins considerably excised, most thickly clothed with spines.

Mandibles, with three strong teeth, two unequal-sized small teeth being placed between the first and second, thus making five altogether; inferior angle broad, pectinated.

Maxillæ, with its edge broad, straight, bearing about twenty pairs of spines, shorter than the large upper spines.

Outer Maxillæ, with the bristles in front, continuous, and without any notch; exterior surface with a prominence clothed with long spines. Olfactory orifices slightly prominent.

Cirri.—First cirrus placed near to the second; posterior cirri not much elongated, with their segments slightly protuberant, bearing four pairs of spines, of which the lower pair is small; spines slightly serrated. In the lower segments, these spines are exceedingly unequal in length, the inner spines on both rami, not being above one fourth of the length of the outer corresponding spine in each pair. The tufts intermediate between these pairs, are not very large: on the lateral upper rims there are some strong, short spines: dorsal tufts with short, thick spines. First cirrus about three fourths as long as the second cirrus, with numerous tapering segments, three or four of the lower ones being thick and protuberant: in the first cirrus there are eleven segments, and in the sixth cirrus, seventeen. Second cirrus, with the anterior ramus slightly thicker than the posterior ramus: a few of the basal segments of both rami are protuberant, and thickly clothed with spines. In the third cirrus, the two rami are nearly equally thick, with some of the basal segments in both clothed, like a brush, with spines. In these brushes on the first, second, and third cirri, most of the spines are doubly toothed, each tooth being simply conical.

Caudal Appendages, small, much flattened, straight on the exterior side, and curved on the inner side, with a row of short, rather thick spines on the crest, and a few on the exterior margin.

The Affinities of this species will be given under the head of the following, P. sertus.

6. Pollicipes sertus. Pl. VII, fig. 5.

P. capitulo valvarum uno aut pluribus sub-rostro verticillis instructo: laterum pari superiore vix inferioribus longiore: membranâ valvas tegente (post desiccationem) fusco rufescente obscuro: rostro dimidiam carinæ longitudinem æquante, superficiei internæ altitudine latitudinem plus duplo superante: pedunculi squamis inæqualibus, non symmetricis: verticillis longiusculè distantibus.

Capitulum with one or more whorls of valves under the rostrum: upper pair of latera only slightly larger than the lower latera: membrane covering the valves (when dried) dark reddish-brown: rostrum half as long as the carina, with its inner surface more than twice as high as broad: scales of peduncle of unequal sizes, unsymmetrically arranged in rather distant whorls.

Maxillæ with two tufts of fine bristles, separated by larger spines: caudal appendages uniarticulate: filamentary appendages none.

New Zealand; Mus. Cuming.

Capitulum, much flattened, broad, sub-triangular. Valves exceedingly various in number; in the largest specimen with a capitulum 8/10ths of an inch high, and 9/10ths of an inch wide, there were only thirty-one valves, and these formed only a single whorl under the carina and rostrum; whereas, in another specimen, which was barely 6/10ths of an inch in length, there were fifty-two valves, and these formed two or three distinct whorls under the carina. Scuta, terga, carina, and rostrum, much larger than the other valves. All are moderately thick, placed rather distant from each other, covered with thick membrane which abounds with tubuli, arranged in rows; surface apparently smooth, but with a very high power, extremely minute spines can be seen at the extremities of almost all the tubuli. Little bunches of reddish fibrous matter are imbedded in the membrane, like tufts of sea-weed floating in water.

Scuta, triangular, basal margin curved, protuberant; the upper part of the tergo-lateral margin is, also, slightly protuberant.

Terga, large, oval, basal angle broad, square; lower part of carinal margin straight, upper part narrowed in; the apex is covered with membrane and projects freely.

Carina, triangular, internally deeply concave, either straight, and with the apex free, or inwardly and considerably curved; basal margin nearly straight.

Rostrum, about half the length of the carina; either straight or inwardly curved; it projects freely for full half its length; inner growing surface triangular, more than twice as high as wide; basal margin very slightly hollowed out. The sub-carina and sub-rostrum are larger than the largest of the latera; their inner surfaces are transversely elongated, rounded at both ends, and slightly concave; externally they are pointed, and project outwards; sometimes the sub-carina, and sometimes the sub-rostrum is the largest.

Latera, small, with their inner surfaces transversely elongated, the larger being the most elongated. Externally they are acuminated, and directed upwards; they project but very little beyond the thick membrane in which they are imbedded. Neither the number, size, nor shape of the latera agree on opposite sides of the same individual; and it would appear that, occasionally, some of them cease to grow, and disappear. In the large specimen with only thirty-one valves, the three pairs of latera, corresponding to the upper, rostral, and carinal latera in Scalpellum, were larger in a marked manner than the others; but in the specimen with fifty-four valves, this could hardly be said to be the case. In this latter specimen, some of the valves in the lowermost whorl were exceedingly minute.

Peduncle, broad, about as long as the capitulum; surface of attachment wide; calcareous scales minute, placed in transverse rows, which become less and less regular in the lower part. The scales do not stand very close together; they are of unequal sizes and irregular outline; generally spindle-shaped; calcareous matter is added regularly only to the scales in the uppermost row, and irregularly to some of the lower scales. The latter, consequently, are the largest, and often much elongated; they are sometimes of singular and irregular shapes.

Colour.—The membrane covering the valves and forming the peduncle, (after having been long kept dry, and not having been in spirits,) is dark reddish chocolate-brown; corium of sack dark purple; cirri banded with dark purplish-brown, with the lower parts of the trophi similarly coloured.

Filamentary Appendages, none, but on the prosoma there are scattered some small papillæ, which are roughened by finely spinose scales, like combs; these papillæ certainly seem to represent the filaments in Pollicipes cornucopia and its two allies.

Ovigerous Fræna, seated in the same position as in P. spinosus, but rather longer, with an elliptical tuft of glands on the crest.

Mouth, not placed far from the adductor muscle.

Labrum, moderately bullate, with the upper part not overhanging; no teeth on the crest. Palpi, short, broad, blunt.

Mandibles, with three main teeth, with either one or two smaller teeth inserted between the first and second, making four or five altogether; inferior angle rather narrow, pectinated with long and fine spines.

Maxillæ, rather broad, with two long upper spines; beneath which there is a very small prominence bearing a minute tuft of fine bristles; beneath this, there are eleven pairs of rather long and strong spines; and the inferior angle is formed by a rather broad, upraised, and obliquely rounded prominence, bearing a broad tuft of fine spines.

Outer Maxillæ, with the inner surface continuously clothed with short spines; exteriorly there is a slight prominence with long hirsute spines.

Olfactory Orifices barely prominent.

Cirri.—First pair placed near the second; the segments of the three posterior pairs are slightly protuberant, and bear three or four pairs of finely serrated spines; intermediate tufts long, the middle spines being the longest; spines on the upper lateral edges long and strong; dorsal tufts rather short. First cirrus, long, multiarticulate, having fourteen or fifteen segments, whilst the sixth cirrus had nineteen segments; rami unequal in length by about two segments; basal segments protuberant brush-like. Second and third cirri with five basal segments of both rami protuberant and brush-like; but the anterior rami in both cirri are broader than the posterior rami. Spines on the protuberant segments of both rami of both cirri, coarsely and doubly pectinated.

Caudal Appendages (Pl. X, fig. 19), minute, uniarticulate, club-shaped, with the enlarged ends directed inwards, or towards each other; summits sparingly clothed with very short spines.

Penis, small.

Affinities.—This species makes a very close approach in the general form and relative sizes of all the valves, and in the variability of the number of the whorls, to P. spinosus; there is a still closer and more important resemblance, in the inequality and manner of growth of the calcareous scales on the peduncle. These species differ, in the colour of the membrane covering the valves, and in the greater development of both rostrum and sub-rostrum in P. sertus. The rostrum of the latter is longer than half the length of the carina, and its inner surface is more than twice as high as wide; and the sub-rostrum is twice as large as any of the latera,—all points of difference from P. spinosus.

In the characters of the mandibles, and more especially of the outer maxillæ; in the length of the first pair of cirri; in both rami of the second and third cirri having their basal segments brush-like, with pectinated spines; and in the shape of the caudal appendages, there is a close relationship to P. spinosus, and through this species to Scalpellum villosum. In the little prominence of the olfactory orifices, P. sertus differs from most of the allied forms, excepting P. spinosus. In the maxillæ having two prominences bearing fine tufts of bristles, in the roughened knobs on the prosoma, and in the presence, in some individuals, of two or three whorls of valves under the carina and rostrum, there is a marked tendency in P. sertus to approach P. cornucopia, P. elegans, and P. polymerus.

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.

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.

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; œsophagus 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.