Very depressed, striated, sometimes with marks of division into four pieces; operculum bivalve. _C. verruca._ The warted Creusia. Pl. 4, fig. 2. Whitish, slightly depressed, with interwoven obliquely striated valves; the margin at the base irregularly serrated. 6. Pyrgoma. One species. The principal difference between this genus and the Creusia is in form. Shell sessile, rather globular appearance on account of the valves being more closely united, ventricose, convex above, apex perforated, aperture small and elliptical; operculum bivalve. _P. cancellata._ The cancellated Pyrgoma. Thick, conical, Patella-shaped, ribs radiating from the summit to the base; aperture very small, closed by an operculum of which the two pieces are long and narrow on each side; pale violet colour. 7. Anatifera. Five species. The shells of this genus and the three following genera are affixed to marine bodies by a tough membranous peduncle, varying in length. Shell flat, with five valves imbricating more or less on the edges, united by a thin membrane. Anatifera lævis. A. villosa. A. dentata. A. striata. A. vitrea. _A. lævis._ The smooth Anatifera. Pl. 4, fig. 5. Five smooth valves; the dorsal one rounded at the sides, and slightly carinated; peduncle long, naked, of a scarlet colour. 8. Pollicipes. Three species. Easily distinguished by the numerous small valves situated at the base. Pollicipes cornucopia. P. mitella. P. scalpellum. _P. cornucopia._ The Cornucopia Pollicipes. Pl. 4, fig. 6. Peduncle covered with imbricated scales, the lower ones rounded and turned upward. _P. mitella._ The Mitre Pollicipes. Pl. 4, fig. 4. Valves indefinite in number, from six to twenty-four; almost equal, and open like tulips; colour bluish, purplish, brownish, or reddish cast. 9. Cineras. One species. Shell composed of five testaceous oblong valves, separate, not covering the whole of the body; two at the sides of the aperture, the others on the back; peduncle of a greenish colour, with six longitudinal stripes. _C. vittata._ The filleted Cineras. Answers to the above description. 10. Otion. Two species. Shell composed of two testaceous valves, enclosed in a mantle or membranous bag, which is prolonged and terminated in two fleshy tubes formed like ears, one of the two having a lateral opening. Otion Cuvierii. Otion Blainvillii. _O. Cuvierii._ Cuvier’s Otion. Answers to the above. _O. Blainvilli._ Blainville’s Otion. Ash coloured; the body and ears spotted with black. CLASS III. CONCHIFERA.