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.

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.

Valves thin, white, translucent; upper layers of growth well preserved, excepting on the terga. A large portion of the carina projected freely. The teeth on the projecting margins of the growth-layers are broad, blunt, and often stand rather distant from each other.

Scuta (Pl. VIII, fig. 3 a), triangular, internally concave with no distinct pit for the adductor muscle. The scuta largely overlap the terga.

Terga (fig. 3 b) approaching to rhomboidal; basal angle rectangular, almost central, and consequently the exterior longitudinal ridge, which is rounded, is likewise nearly central.

Carina, internally concave, with no trace of a central internal ridge in the upper free portion; the growing or corium-covered surface is transversely oval, and is as wide as the widest part of the terga.

Rostrum, exceedingly minute, enlarged at each zone of growth, not so wide as the immediately subjacent scale on the peduncle.

Latera (fig. 3 c), in width equalling two and a half of the upper peduncular scales, or about one fourth or one fifth of the width of the carina; growing surface, (or a section parallel to the layers of growth,) broadly elliptic, pointed at both ends.

Peduncle, about twice as long as the capitulum; the scales of the uppermost whorl are quadrilateral (fig. 3 d), and nearly four times as large as those in the second whorl; these latter are about twice as large as those in the third whorl, which are very little larger than the small, almost equal-sized, equally distant, round beads scattered over the rest of the peduncle, down to the basal cup. All these scales are dentated, the upper rows most plainly and only on their basal margins; the lower little beads are very slightly crenated round their entire margins; they are mingled with star-headed spines (fig. 3 e) of yellow chitine. Basal calcareous discs thin, plainly marked exteriorly by concentric lines of growth, and covered by the usual yellow membrane, including the horny, spindle-shaped bodies.

Size and Colours.—The whole specimen, including the peduncle, was only one fifth of an inch in length; the capitulum being 3/40ths of an inch in width. I do not know whether the specimen had attained its full size, but think this is probable, as a large-sized species would not have made its habitation in one of the valves of so small a shell as a Conia. Shell white, exterior membrane, where preserved, yellow, and bearing small spines. Thoracic segments, the lower segments of the second, third, and fourth cirri, all the segments of the first cirrus and the trophi, slightly mottled with darkish purple.

Mouth.—The teeth or beads on the crest of the labrum are blunt, few, not very small, and equidistant.

Palpi, bluntly pointed.

Mandibles, with the three main teeth nearly equal in size; the pectinations are equal in number, namely, only three between the first and second, and the second and third main teeth; the inferior angle is coarsely pectinated, with one central spine much longer than the others; the distance between the tips of the first and second main teeth, equals that between the second tooth and the inferior angle.

Maxillæ, with the two upper spines very large; beneath them there are two small spines, and a considerable notch; the inferior part of the edge is nearly straight, bearing about thirteen pairs of spines, obscurely divided into two groups, the lower spines being smaller than the upper ones. The upper convex margin is hirsute with long hairs.

Outer Maxillæ, blunt, with the inner margin slightly concave; continuously, but thinly clothed with spines.

Cirri.—The segments of the three posterior pairs bear four pairs of spines, with the usual intermediate fine spines; dorsal spines thin and thick mingled together. First cirrus, short, with the anterior ramus rather the thickest and shortest; all the segments thickly paved with bristles, except the two terminal segments, of which the ultimate one bears some serrated spines of most unusual length, namely, equalling within one segment the entire length of the ramus. I presume that these spines serve as feelers. Second cirrus; anterior ramus much thicker and considerably shorter than the posterior ramus; six basal segments paved with bristles, the two terminal segments having the usual structure; posterior ramus with all its nine segments on the usual structure. Third cirrus, longer, to a remarkable degree, than the second cirrus, with its anterior ramus having the four basal segments paved, and the seven terminal ones on the usual structure; posterior ramus with twelve segments, of which none are paved. The pedicels of the second and third cirri thickly and irregularly clothed with spines. The upper segments of the pedicels of all the cirri are unusually long.

Caudal Appendages, longer than the pedicels of the sixth cirrus, by barely one third of their own length. Segments much elongated, seven in number; I may add for comparison that each ramus of the sixth cirrus contained, in this specimen, sixteen or seventeen segments.

General Remarks.—It is difficult to give obvious characters, (excepting the smallness of the rostrum compared with the scales on the peduncle,) by which this species can be externally discriminated from L. dorsalis, L. Nicobarica, and L. Rhodiopus; yet almost all the valves differ slightly in shape. In this species alone, (the peduncle of L. Rhodiopus is not known,) the lower, microscopically minute, bead-like scales of the peduncle are crenated, though obscurely, all round. In the animal’s body, the diagnostic characters are strongly marked;—the long spines on the terminal segment of the first cirrus,—none of the segments in the posterior rami of the second and third cirri being thickened and paved with bristles,—the pectinations being equal in number between the main teeth of the mandibles,—are all characters exclusively confined to this species.

3. Lithotrya nicobarica. Pl. VIII, fig. 2.

L. scutis terga angustè obtegentibus: carinæ cristâ internâ tenui in parte superiore positâ: rostro conspicuo, squamarum sex subjacentium latitudinem æquante: lateribus, superficie internâ triangulâ, squamarum septem subjacentium latitudinem æquantibus.

Scuta narrowly overlapping the terga: carina with a slight central internal ridge in the upper part: rostrum conspicuous, as wide as six of the subjacent scales: latera, with their internal surfaces triangular, as wide as seven of the subjacent scales.

Palpi square at their ends: mandibles with twice as many pectinations between the first and second main teeth, as between the second and third: maxillæ slightly notched, with the inferior angle slightly prominent: caudal appendages more than twice as long as the pedicels of the sixth cirrus.

Capitulum as in L. dorsalis. The teeth on the prominent rims of the valves are small and approximate; but the specimen was much worn.

Scuta, triangular, slightly overlapping the terga; the line of junction between these valves slightly sinuous, the upper part of the tergal margin of the scuta being slightly hollowed out, and the corresponding upper portion of the margin of the terga being slightly protuberant. Internally, there is a considerable depression for the adductor muscle; and besides the usual knob at the rostral angle, there is a trace of a knob at the baso-tergal angle.

Terga, as seen internally, irregularly rhomboidal, ending downwards in a blunt point, of which the two sides, (neither being sensibly hollowed out,) stand at about an angle of 45° to each other. Scutal margin, with the upper part, (as above remarked,) slightly protuberant: near the bottom of this margin, there is a very slight projection, answering to the small knob at the baso-tergal angle of the scutum. Externally, towards the basal angle, the narrow strip not concealed by the overlapping of the latera and carina is square-edged, with the zones of growth on it straight.

Carina, internally concave in the upper free part, with a slight, central, internal crest, caused by the projection of each successive zone of growth. The inner growing surface is almost pentagonal in outline; with the basal margin square and truncated in the middle.

Rostrum (fig. 2 a), rather conspicuous, many zones of growth being preserved. It equals in width six of the subjacent scales of the peduncle, but as these are rather smaller than elsewhere, the width equals about five of the ordinary uppermost scales; compared with the latera, it is nearly 5/7ths of their width.

Latera, unusually large; as seen on their interior surfaces, (or in a section parallel to the zones of growth,) they are triangular, elongated transversely, with the carinal angle a rectangle. In width they equal the seven subjacent scales of the peduncle, and are more than half as long as the basal margin of the carina.

Peduncle, with the upper scales varying from circular to quadrilateral, thrice as large as those in the second whorl; beneath which, in the next three or four whorls, the scales rapidly decrease in size; and beneath these the whole peduncle is studded with equal-sized, rounded, calcareous beads, so minute as to be quite invisible to the naked eye. This specimen was nearly ready to moult, and perhaps in consequence of this, even the upper scales were most obscurely serrated on their lower margins, and all the others quite smooth: there were some much worn horny spines close to the bottom of the peduncle. Basal calcareous cup slightly concave, of moderate size; its diameter, in the one specimen examined, was 9/10ths of an inch; it was composed of several layers. In the specimen figured (2 a´) by Reinhardt, instead of a cup, there is a straight row of small discs, which are attached to the walls of the cavity, as explained in the generic description.

Mouth.—Palpi with their ends square and truncated; thickly clothed with long spines.

Mandibles, with fully twice as many pectinations, (viz. from 16 to 20,) between the first and second main teeth, as between (viz. 8 to 10) the second and third main teeth. Inferior angle, coarsely pectinated. The distance between the tips of the first and second teeth, is considerably less than between the tip of the second tooth and the inferior angle.

Maxillæ, with the edge very slightly irregular; beneath the two great upper spines there is a slight notch, with some small spines: inferior angle slightly prominent, with a brush of moderately fine spines; besides these, there are about seventeen pairs of large spines; sides very hairy.

Outer Maxillæ, with the inner margin slightly concave, and with the spines continuous.

Cirri.—The segments in the three posterior pairs support three or four pairs of long spines, with a single row of moderately long intermediate spines; the dorsal tufts consist of a few rather thick, and some long and thin spines. The front of the segments is not protuberant; the whole surface is hirsute with minute comb-like scales. Second cirrus, with the anterior ramus having its eight basal segments highly protuberant and thickly clothed with spines, the upper nine having the usual structure; the posterior ramus has four or five basal segments thickly clothed with spines, and the twelve upper ones with the usual structure. Third cirrus, with the anterior ramus having six segments highly protuberant and thickly clothed with bristles, and the fifteen upper ones on the usual structure; in the posterior ramus, only three or four of the basal segments are paved with bristles. The spines on the first three pairs of cirri, are coarsely and doubly serrated.

The Caudal Appendages are more than twice as long as the pedicels of the sixth cirrus, and equal half the length of the whole cirrus. In a specimen in which the sixth cirrus contained twenty-two segments, the caudal appendages actually contained twenty. The segments are thin, with their upper edges clothed with serrated spines. The slip of membrane on each side, whence this organ springs is united, for a little space, to the lower segment of the pedicel of the sixth cirrus.

Size and Colour.—Width of the capitulum rather above 4/10ths of an inch; length, including the peduncle, (contracted by spirits,) nearly one inch. Valves, as usual, dirty white, partly invested by yellow membrane, furnished with a few minute yellow horny spines. Pedicels of the first four cirri, caudal appendages, penis, the two posterior thoracic segments, the segments of the cirri, and the trophi, clouded, banded, or spotted, with blackish purple.

Affinities.—This species, in the characters derived from the valves, comes perhaps nearest to L. Rhodiopus; in the characters derived from the animal’s body, it is nearest to L. dorsalis.

4. Lithotrya rhodiopus. Pl. VIII, fig. 4.

L. scutis terga ample obtegentibus: carinæ cristâ internâ tenui, in parte superiore positâ: lateribus, superficie internâ symmetricè et latè ovatâ, carinæ latitudinis plus quam tertiam partem æquantibus: tergorum basali apice tenui, et angulo carinali producto: rostro et pedunculo ignotis.

Scuta largely overlapping the terga. Carina with a slight central internal ridge in the upper part. Latera with their internal surfaces symmetrically and broadly oval, more than one third of the width of the carina. Terga with the basal points narrow, and the carinal angle produced. Rostrum and peduncle unknown.

Mandibles, with four times as many pectinations between the first and second main teeth, as between the second and third; distance greater between the tips of the first and second teeth, than between the tip of the second tooth and the inferior angle. Maxillæ widely notched, with the inferior part forming two obscure prominences.

The specimens are in a rather bad condition, and have been disarticulated. They are of rather small size; the rostrum and peduncle are lost, and animal’s body much injured.

Valves white, thin, translucent; teeth on the projecting rims small, narrow, standing further apart than their own width. The upper layers have undergone but little disintegration or scaling off, and consequently the carina and terga project freely. The valves, where not rubbed, are covered by bright yellow membrane, which is thickly clothed with rows of spines; these are small on the exterior surfaces, but are very large and hooked in certain parts, as near the tergal margins of the scuta, and on the carinal margins of the terga, and especially on the inner face of the upper free part of the carina. Here the hooked spines (fig. 4 d) are trifid or quadrifid, and are very conspicuous.

Scuta, as seen externally, triangular; they overlap half the width of the terga; on their internal faces (fig. 4 a), in the upper projecting part, there is a strong ridge, against which the scutal margin of the terga abuts. There is a deep and conspicuous pit for the adductor muscle.

Terga, as seen externally, nearly triangular. The ridge which leads from the apex to the basal angle, is rounded, central, and extremely prominent; but does not form a furrow, or include the overlapping margin of the scuta. The basal angle is narrow, spur-like, and slightly hollowed out on both margins. The growing corium-covered surface (fig. 4 b) is transversely elongated, with the occludent margin rounded, and the carinal angle much produced, but not forming a roughened knob.

Carina (fig. 4 d), concave within, with a slight central ridge in the upper free portion. The inner growing surface is concave, almost pentagonal, with a just perceptibly raised central rim in the upper part, and with two minute prominences on each side, against which the produced carinal angles of the terga abut.

Rostrum, lost.

Latera (fig. 4 c), growing surface (or a section parallel to the growth-layers,) symmetrically oval, more than one third as wide as the basal margin of the carina. Several zones of growth preserved.

Peduncle, lost, but a few scales accidentally adhering to one of the valves, show that they are crenated in the three or four upper whorls. No basal calcareous cup was preserved, but by clearing out the base of one of the holes in the coral, in which a specimen had been imbedded, I found a little flat disc about the size of a pin’s head; it was composed of two or three layers, and was externally coated by yellow membrane, including the usual spindle-shaped bodies and tubuli. The cement-ducts were also discovered after dissolution in acid. So that there could be no doubt regarding the nature of the little disc.

Mouth.—Labrum with a row of little blunt teeth.

Palpi, blunt, rather expanded at their ends, with the extreme margin much arched and furnished with two rows of long spines; there is a fringe of short spines on the straight inner side.

Mandibles.—There are nine pectinations between the first and second main teeth, and only two between the second and third teeth; the inferior angle is coarsely pectinated, with one central spine twice as long as the others. The distance between the tips of the first and second main teeth, is greater than between the tip of the second tooth and the inferior angle.

Maxillæ (Pl. X, fig. 12).—These may be described as having their edge formed into three prominences; or, as having a very wide notch under the two upper great spines, and with the whole inferior part forming two prominences. There are, altogether, about twelve pairs of spines, of which two stand singly on the inferior side of the wide notch under the two upper great spines. The spines on the inferior angle are rather smaller than those above; sides hirsute.

Outer Maxillæ, with the inner margin slightly concave, and sparingly covered with bristles.

Cirri, imperfectly preserved; the three posterior pairs have segments of the usual character, bearing five pairs of very long spines, with the usual little intermediate, the minute lateral, and the dorsal spines. First cirrus lost; second and third with only their few basal segments preserved, sufficient, however, to show that at least two or three segments, in both the anterior and posterior rami of both cirri, were paved with bristles.

Pedicels, as in the other species.

Caudal Appendages, lost.

This species comes very close, as far as the characters derived from the trophi serve, to the L. truncata, though readily distinguished from that species by the shape of the valves. On the other hand, the capitulum of this species is distinguished with difficulty from that of L. Nicobarica and L. cauta; no doubt this difficulty is much enhanced by the rostrum and peduncle having been lost.

5. Lithotrya truncata. Pl. IX, fig. 1.

L. scutis in profundam tergorum plicam insertis: carinæ cristâ centrali prominente et rotundatâ in parte superiore: rostro et lateribus rudimentalibus, carinæ latitudinis quindecimam fere partem æquantibus.

Scuta locked into a deep fold in the terga: carina with a prominent central rounded ridge in the upper part: rostrum and latera rudimentary, about 1/15th of the width of the carina.

Mandibles, with nearly three times as many pectinations between the first and second teeth, as between the second and third teeth; distance between the tips of the first and second teeth equal to that between the tip of the second tooth and inferior angle. Maxillæ widely notched, with the inferior part forming two prominences. Caudal appendages shorter than, or barely exceeding in length, the pedicels of the sixth cirrus.

Capitulum rather thick, with the five main valves having their free apices, diverging and truncated. The upper and old layers of shell do not here scale off so readily as in many of the foregoing species; and hence an unusually large proportional length of each valve projects freely above the sack; and the valves are of unusual thickness. The capitulum is very nearly as wide at its summit as at its base, owing to the divergence of the apices of the valves. The scuta and terga are articulated together by a conspicuous fold, which, when seen from vertically above, (Pl. IX, fig. 1 a´,) appears like a deep wedge-formed notch in the terga. On the exterior surfaces of the valves, the teeth on the successive rims are approximate; on the inner surfaces, the rims are covered by strong yellow membrane, which is generally fringed with small horny spines.

Scuta, exterior surface convex, sub-triangular, with the apex truncated: seen vertically from above, there is a small rectangular indentation or fold which receives the projecting scutal margin of the terga. The inner growing or corium-covered surface (fig. 1 b, b´) is triangular, with its tergal margin largely hollowed out. Along the occludent margin there is a slight ridge, which terminates at the rostral angle, in both the right and left-hand valves, in a rounded, knob-like, roughened tooth. The lower part of the tergal margin is slightly inflected and roughened, where it meets the corresponding lower part of the scutal margin of the terga. There is a deep pit for the adductor muscle. The interior surface of the valve above this pit is faintly-coloured purple. The inner surfaces of both scuta and terga, are roughened with little points.

Terga, seen externally, are almost quadrilateral (owing to the apex being truncated), with the free margin facing the scutum, arched. Seen vertically from above, each shows a deep fold, which receives the lower part of the tergal margin of the scutum. In the foregoing species, a prominent ridge runs down the exterior surface of the terga from the apex to the basal angle, against which ridge, the margin of the overlapping scuta abuts: here this ridge, instead of projecting straight out, is oblique or folded over, and thus forms a furrow, receiving the margin of the scuta. The interior growing surface of the tergum (fig. 1 b´, c), presents so irregular a figure, that it can hardly be described; in area it quite equals the scuta; it is slightly concave; at the upper point of the carinal margin, there is a large, rounded, protuberant, roughened knob, which corresponds with a small knob on each side of the inner face of the carina; these knobs seem firmly united together by membrane. The scutal margin of the terga, in the upper part, forms a shoulder, largely projecting over the scuta; on its lower part, there is a small roughened projection. The occludent margin is arched and protuberant, with a slight fold above the knob on the carinal margin, just mentioned: this fold is caused by the protuberance of the central internal ridge of the carina, but is so small, that when the capitulum is seen from vertically above, it can hardly be distinguished. Finally, the basal half of the carinal margin, runs in the same line with the basal margin of the scuta.

Carina, moderately large; seen externally, the surface presents an elongated triangle, with the apex truncated; on the internal face (fig. 1 b´, d) of the free part, there is (instead of being concave as is usual) a great central ridge, which projects between the diverging apices of the terga, as may be seen from vertically above; hence the thickness of the upper part of the carina, in a longitudinal plane, almost equals its breadth. The edge of this ridge is rounded. The inner or growing surface of the carina is tinted purple, and lies in a plane, oblique to the longer axis of the valve; it is triangular, with the apex cut off, and the basal margin rounded and protuberant; it is not concave. There is a central raised line or slight ridge on this inner surface, and on each side in the upper part there is a small, white, roughened knob, corresponding with the similar knobs on the carinal margins of the terga.

Rostrum (fig. 1 b´, a), rudimentary; in one specimen it was about 1/50th of an inch in width; it is either as wide, or only half as wide, as the subjacent scale on the peduncle.

Latera, rudimentary, placed between the edges of the carina and the terga; rather smaller than the rostrum; almost cylindrical, slightly flattened, enlarged at each zone of growth, with one or two sharp teeth or spines on both faces; imperfectly calcified; in width barely 1/15th part of the carina.

Peduncle, short; the scales alone in the uppermost whorl are plainly toothed; they are transversely elongated, and almost quadrangular, and are nearly twice as large as those in the second whorl. Beneath this second whorl, there are two or three whorls, with scales, graduated in size; and the rest of the peduncle is covered by rather distantly scattered, minute, rounded or acutely pointed scales: the pointed scales are directed upwards, and are best developed under the carina. The basal calcareous cup, judging from two specimens, is thin, and not much developed.

Size and Colour.—The largest specimen was nearly 6/10ths of an inch across its capitulum. The calcareous valves are dirty white. The sack is (after having been long kept in spirits) pale coloured, excepting a small purple space, between the scuta and another over the carina. The three posterior segments of the thorax and portions under the second and third cirri, the trophi, the pedicels and the anterior faces of the segments (especially of the basal segments in the second and third cirri), and a spot on their dorsal surfaces, and the penis are all coloured dark purplish-black. The prosoma is pale coloured.

Mouth.—Crest of labrum with a row of bead-like teeth and hairs. Palpi bluntly pointed, with neither margin hollowed out.

Mandibles, with eight pectinations between the first and second main teeth, and three between the second and third teeth; inferior angle coarsely pectinated, with a central spine much longer than the others; the distance between the tips of the first and second main teeth, is about equal to that between the tip of the second tooth and of the inferior angle.

Maxillæ.—Under the two upper long spines (associated with some smaller ones), there is a slight and wide hollow; and the whole inferior edge obscurely forms two blunt points, with the spines on the lower projection smaller than the upper spines.

Outer Maxillæ, considerably concave in front, with the spines almost discontinuous in the middle part.

Cirri.—First pair rather far separated from the second pair. The segments of the three posterior cirri bear three or four pairs of main spines, and are otherwise characterised like the foregoing species. First cirrus, with its anterior ramus much thicker than the posterior ramus, and of nearly equal length; all the segments, except the two terminal ones, thickly clothed with serrated spines. Second cirrus considerably shorter than the third cirrus: anterior ramus with the seven basal segments very protuberant, and paved with bristles, and the four terminal ones on the usual structure; posterior ramus, with the five basal segments paved (but much less thickly than in the anterior ramus), and the nine terminal ones on the usual structure. Third cirrus, the anterior ramus, with the five basal segments, thick and paved, and eleven terminal segments on the usual structure: posterior ramus, with one basal segment paved, and sixteen other segments on the usual structure. In the posterior rami, however, of both the second and third cirri, it is difficult to draw any distinct line between the paved segments and the others.

Caudal Appendages, short, either just exceeding in length the pedicels of the sixth cirrus, or equalling only the lower segment: segments flattened, cylindrical, six in number, there being, in the same individual, twenty-one segments in both rami of the sixth cirrus.

6. Lithotrya Valentiana. Pl. VIII, fig. 5.

L. scutis in profundam tergorum plicam invertis: tergorum opposito superiore margine, plicâ alterâ æquè profundâ instructo: carinæ cristâ prominente centrali, marginibus quadratis, in parte superiore: rostro rudimentali: lateribus et pedunculo ignotis.

Scuta locked into a deep fold in the terga; the latter having a second equally deep fold on the opposite upper margin. Carina with a prominent, central, square-edged ridge in the upper part: rostrum rudimentary. Latera and peduncle unknown.

Animal unknown.

General Remarks.—The two specimens in the British Museum are small, and in an imperfect condition, without the peduncle or the latera, and without the body of the animal. The capitulum so closely resembles that of L. truncata, that it is quite superfluous to do more than point out the few differences. It is just possible, though not probable, that this form may prove to be merely a variety or younger state of L. truncata, in which case this latter name would have to be sunk. The difference, though one only of degree, in the form of the terga of the two species is conspicuous, and there is a slight difference in the carina, and again some dissimilarity in habits.

Description.—The valves, as just stated, generally resemble those of L. truncata; scarcely any appreciable difference can be detected in the scuta; the apex, however, of the inner surface seems coloured a darker purple. The terga, as seen from vertically above (Pl. VIII, fig. 5 b), have a fold or indentation on the upper or occludent margin, as large and as conspicuous as that receiving the margin of the scuta: this fold, as seen on the inner corium-covered surface (fig. 5 a), descends below the roughened knob at the upper angle of the carinal margin, which is not the case with the slight fold in the same place in L. truncata; its presence seems caused by the edge of the central internal crest, in the upper part of the carina, being square (instead of round, as in L. truncata), and thus more deeply affecting the outline of the terga, between which it is inserted. The upper part of the scutal margin of the terga, as seen internally (fig. 5 a), overlaps the scuta in a large rectangular projection. From the depth of the two opposite folds, namely, that caused by the tergal edge of the scuta and that by the crest of the carina, the inner face of the tergum is divided into two almost equal areas. The carina has its central crest square (fig. 5 c, d,) instead of being rounded as in L. truncata. The inner growing or corium-covered face is nearly at right angles to the longitudinal axis of the whole valve, instead of being oblique to it; it is convex or protuberant, with a central raised line, and two little knobs on each side of the upper part; the two lateral margins are slightly hollowed out, and the basal margin is not highly protuberant. The rostrum is excessively minute, barely above 1/200th of an inch in width; it is a little enlarged at each zone of growth. Latera lost; no doubt they were rudimentary.

A fragment of a posterior cirrus, which adhered to one of the valves, shows that each segment supported four pairs of spines.

Width of the capitulum before disarticulation, probably was about 1/10th of an inch.

Species mihi non satis notæ, aut dubiæ.