_Cirri._--The segments of the three posterior pairs bear four pairs of spines, with the usual intermediate fine spines; dorsal spines thin and thick mingled together. _First cirrus_, short, with the anterior ramus rather the thickest and shortest; all the segments thickly paved with bristles, except the two terminal segments, of which the ultimate one bears some serrated spines of most unusual length, namely, equalling within one segment the entire length of the ramus. I presume that these spines serve as feelers. _Second cirrus_; anterior ramus much thicker and considerably shorter than the posterior ramus; six basal segments paved with bristles, the two terminal segments having the usual structure; posterior ramus with all its nine segments on the usual structure. _Third cirrus_, longer, to a remarkable degree, than the second cirrus, with its anterior ramus having the four basal segments paved, and the seven terminal ones on the usual structure; posterior ramus with twelve segments, of which none are paved. The pedicels of the second and third cirri thickly and irregularly clothed with spines. The upper segments of the pedicels of all the cirri are unusually long.
_Caudal Appendages_, longer than the pedicels of the sixth cirrus, by barely one third of their own length. Segments much elongated, seven in number; I may add for comparison that each ramus of the sixth cirrus contained, in this specimen, sixteen or seventeen segments.
_General Remarks._--It is difficult to give obvious characters, (excepting the smallness of the rostrum compared with the scales on the peduncle,) by which this species can be externally discriminated from _L. dorsalis_, _L. Nicobarica_, and _L. Rhodiopus_; yet almost all the valves differ slightly in shape. In this species alone, (the peduncle of _L. Rhodiopus_ is not known,) the lower, microscopically minute, bead-like scales of the peduncle are crenated, though obscurely, all round. In the animal"s body, the diagnostic characters are strongly marked;--the long spines on the terminal segment of the first cirrus,--none of the segments in the posterior rami of the second and third cirri being thickened and paved with bristles,--the pectinations being equal in number between the main teeth of the mandibles,--are all characters exclusively confined to this species.
3. LITHOTRYA NICOBARICA. Pl. VIII, fig. 2.
L. NICOBARICA. _Reinhardt_, Naturhist; Selskabet, Copenhagen. No.
I. 1850. Tab. I, fig. 1-3.[68]
[68] I am not at all sure that the proper t.i.tle of the periodical in which this species has been described, is here given. I am greatly indebted to Prof. Steenstrup for sending me a separate copy of the paper in question, written in Danish. I believe I am right in identifying the specimen here described, from Timor, with the species from the Nicobar Islands, named by Reinhardt, _L. Nicobarica_.
_L. scutis terga anguste obtegentibus: carinae crista interna tenui in parte superiore posita: rostro conspicuo, squamarum s.e.x subjacentium lat.i.tudinem aequante: lateribus, superficie interna triangula, squamarum septem subjacentium lat.i.tudinem aequantibus._
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: maxillae slightly notched, with the inferior angle slightly prominent: caudal appendages more than twice as long as the pedicels of the sixth cirrus.
Timor; Brit. Mus., (given by Cuvier to Leach); Nicobar Islands, according to Reinhardt.
Capitulum as in _L. dorsalis_. The teeth on the prominent rims of the valves are small and approximate; but the specimen was much worn.
_Scuta_, triangular, slightly overlapping the terga; the line of junction between these valves slightly sinuous, the upper part of the tergal margin of the scuta being slightly hollowed out, and the corresponding upper portion of the margin of the terga being slightly protuberant. Internally, there is a considerable depression for the adductor muscle; and besides the usual k.n.o.b at the rostral angle, there is a trace of a k.n.o.b 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 k.n.o.b 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 h.o.r.n.y 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, coa.r.s.ely 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.
_Maxillae_, 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 Maxillae_, 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 coa.r.s.ely 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 s.p.a.ce, 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 h.o.r.n.y spines. Pedicels of the first four cirri, caudal appendages, p.e.n.i.s, 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.
BRISNaeUS RHODIOPUS. _J. E. Gray._ Annals of Philosoph., vol. x, (new series,) 1825.
---- ---- _J. E. Gray._ Spicilegia Zoolog., Tab. xvi, fig. 17, 1830.
_L. scutis terga ample obtegentibus: carinae crista interna tenui, in parte superiore posita: lateribus, superficie interna symmetrice et late ovata, carinae lat.i.tudinis plus quam tertiam partem aequantibus: 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. Maxillae widely notched, with the inferior part forming two obscure prominences.
Hab. unknown. Imbedded in a ma.s.sive coral. Brit. Mus.
The specimens are in a rather bad condition, and have been disarticulated. They are of rather small size; the rostrum and peduncle are lost, and animal"s body much injured.
Valves white, thin, translucent; teeth on the projecting rims small, narrow, standing further apart than their own width. The upper layers have undergone but little disintegration or scaling off, and consequently the carina and terga project freely. The valves, where not rubbed, are covered by bright yellow membrane, which is thickly clothed with rows of spines; these are small on the exterior surfaces, but are very large and hooked in certain parts, as near the tergal margins of the scuta, and on the carinal margins of the terga, and especially on the inner face of the upper free part of the carina. Here the hooked spines (fig. 4 _d_) are trifid or quadrifid, and are very conspicuous.
_Scuta_, as seen externally, triangular; they overlap half the width of the terga; on their internal faces (fig. 4 _a_), in the upper projecting part, there is a strong ridge, against which the scutal margin of the terga abuts. There is a deep and conspicuous pit for the adductor muscle.
_Terga_, as seen externally, nearly triangular. The ridge which leads from the apex to the basal angle, is rounded, central, and extremely prominent; but does not form a furrow, or include the overlapping margin of the scuta. The basal angle is narrow, spur-like, and slightly hollowed out on both margins. The growing corium-covered surface (fig.
4 _b_) is transversely elongated, with the occludent margin rounded, and the carinal angle much produced, but not forming a roughened k.n.o.b.
_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 coa.r.s.ely 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.
_Maxillae_ (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 Maxillae_, 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.