The stomach, in those species which I opened, is destitute of cæca; the hepatic glands are arranged in straight lines; the rectum is unusually short. The prosoma is well developed.

In P. cornucopia, P. elegans, and P. polymerus, there are numerous filamentary appendages both on the prosoma, and at the bases of the first pair of cirri: these appendages are occupied by testes, and I suspect stand in relation to the length of the peduncle and consequent great development of the ovaria. In order to give space for the filamentary appendages, the sack (generally roughened by small inwardly-pointing papillæ) penetrates more deeply than usual into the upper part of the peduncle. There are small ovigerous fræna in P. sertus, P. spinosus, and P. mitella: in the three other species, the frænum or fold occupies the usual position on each side, and is large; but in one specimen carefully examined by me, I was unable to see any glands; and in another specimen, the ovigerous lamellæ were not attached to the fræna; hence I conclude that the fræna are functionless in these three species.

Affinities.—I have already remarked on the close relationship between this genus and Scalpellum; there is also some affinity with Lithotrya.

Distribution.—All over the world. The P. cornucopia ranges from Scotland to Teneriffe: the P. polymerus is found in opposite hemispheres in the Pacific Ocean, extending from California to at least as far as 32° south of the Equator.

Geological History.—Having so lately given, in the ‘Memoirs of the Palæontographical Society,’ a full account of all the fossil species known, I will not repeat here the conclusions there arrived at. I will only state, that species of Pollicipes are found in all the formations, extending from the Lower Oolite to the Upper Tertiary beds.

1. Pollicipes cornucopia. [Pl. VII], [fig. 1.]

Pollicipes cornucopia. Leach. Encyclop. Brit. Supp., vol. iii, 1824.

————— Smythii, var. Leach. Ibid.

Lepas Pollicipes. Gmelin. Systema Naturæ, 1789.

————— gallorum. Spengler. Skrivter Naturhist. Selskabet, Bd. i, Tab. vi, fig. 9, 1790.