Brisnæus rhodiopus. J. E. Gray. Annals of Philosoph., vol. x, (new series,) 1825.
—— —— —— —— —— J. E. Gray. Spicilegia Zoolog., Tab. xvi, fig. 17, 1830.
L. scutis terga ample obtegentibus: carinæ cristâ internâ tenui, in parte superiore positâ: lateribus, superficie internâ symmetricè et latè ovatâ, carinæ latitudinis plus quam tertiam partem æquantibus: tergorum basali apice tenui, et angulo carinali producto: rostro et pedunculo ignotis.
Scuta largely overlapping the terga. Carina with a slight central internal ridge in the upper part. Latera with their internal surfaces symmetrically and broadly oval, more than one third of the width of the carina. Terga with the basal points narrow, and the carinal angle produced. Rostrum and peduncle unknown.
Mandibles, with four times as many pectinations between the first and second main teeth, as between the second and third; distance greater between the tips of the first and second teeth, than between the tip of the second tooth and the inferior angle. Maxillæ widely notched, with the inferior part forming two obscure prominences.
Hab. unknown. Imbedded in a massive coral. Brit. Mus.
The specimens are in a rather bad condition, and have been disarticulated. They are of rather small size; the rostrum and peduncle are lost, and animal’s body much injured.
Valves white, thin, translucent; teeth on the projecting rims small, narrow, standing further apart than their own width. The upper layers have undergone but little disintegration or scaling off, and consequently the carina and terga project freely. The valves, where not rubbed, are covered by bright yellow membrane, which is thickly clothed with rows of spines; these are small on the exterior surfaces, but are very large and hooked in certain parts, as near the tergal margins of the scuta, and on the carinal margins of the terga, and especially on the inner face of the upper free part of the carina. Here the hooked spines (fig. 4 d) are trifid or quadrifid, and are very conspicuous.
Scuta, as seen externally, triangular; they overlap half the width of the terga; on their internal faces (fig. 4 a), in the upper projecting part, there is a strong ridge, against which the scutal margin of the terga abuts. There is a deep and conspicuous pit for the adductor muscle.
Terga, as seen externally, nearly triangular. The ridge which leads from the apex to the basal angle, is rounded, central, and extremely prominent; but does not form a furrow, or include the overlapping margin of the scuta. The basal angle is narrow, spur-like, and slightly hollowed out on both margins. The growing corium-covered surface (fig. 4 b) is transversely elongated, with the occludent margin rounded, and the carinal angle much produced, but not forming a roughened knob.
Carina (fig. 4 d), concave within, with a slight central ridge in the upper free portion. The inner growing surface is concave, almost pentagonal, with a just perceptibly raised central rim in the upper part, and with two minute prominences on each side, against which the produced carinal angles of the terga abut.
Rostrum, lost.
Latera (fig. 4 c), growing surface (or a section parallel to the growth-layers,) symmetrically oval, more than one third as wide as the basal margin of the carina. Several zones of growth preserved.
Peduncle, lost, but a few scales accidentally adhering to one of the valves, show that they are crenated in the three or four upper whorls. No basal calcareous cup was preserved, but by clearing out the base of one of the holes in the coral, in which a specimen had been imbedded, I found a little flat disc about the size of a pin’s head; it was composed of two or three layers, and was externally coated by yellow membrane, including the usual spindle-shaped bodies and tubuli. The cement-ducts were also discovered after dissolution in acid. So that there could be no doubt regarding the nature of the little disc.
Mouth. — Labrum with a row of little blunt teeth.
Palpi, blunt, rather expanded at their ends, with the extreme margin much arched and furnished with two rows of long spines; there is a fringe of short spines on the straight inner side.
Mandibles. — There are nine pectinations between the first and second main teeth, and only two between the second and third teeth; the inferior angle is coarsely pectinated, with one central spine twice as long as the others. The distance between the tips of the first and second main teeth, is greater than between the tip of the second tooth and the inferior angle.
Maxillæ (Pl. X, fig. 12). — These may be described as having their edge formed into three prominences; or, as having a very wide notch under the two upper great spines, and with the whole inferior part forming two prominences. There are, altogether, about twelve pairs of spines, of which two stand singly on the inferior side of the wide notch under the two upper great spines. The spines on the inferior angle are rather smaller than those above; sides hirsute.
Outer Maxillæ, with the inner margin slightly concave, and sparingly covered with bristles.
Cirri, imperfectly preserved; the three posterior pairs have segments of the usual character, bearing five pairs of very long spines, with the usual little intermediate, the minute lateral, and the dorsal spines. First cirrus lost; second and third with only their few basal segments preserved, sufficient, however, to show that at least two or three segments, in both the anterior and posterior rami of both cirri, were paved with bristles.
Pedicels, as in the other species.
Caudal Appendages, lost.
This species comes very close, as far as the characters derived from the trophi serve, to the L. truncata, though readily distinguished from that species by the shape of the valves. On the other hand, the capitulum of this species is distinguished with difficulty from that of L. Nicobarica and L. cauta; no doubt this difficulty is much enhanced by the rostrum and peduncle having been lost.