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.]

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.