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._ 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.