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

Conchotrya Valentiana. J. E. Gray. Annals of Philosoph., vol. x (new series), 1825.

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

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

Animal unknown.

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

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

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

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

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