_Shell._ Patella-shaped, sub-conically oval, formed of six lateral unequal valves forming the base, which being convex prevents the shell from standing by itself in an erect position, when detached from the substance which envelopes it. Inhabits the British seas. Four species. Acasta Montaguii. A. sulcata. A. glans. A. tubulosa. 5. Genus _Creusia_. Pl. V. _Animal._ Body, subglobular, inclosed in an operculated shell; having three or four pairs of tentacular arms: mouth at the anterior part of the body. _Shell._ Sessile, fixed, orbicular, conical, consisting of four united unequal valves; attached to madrepore and other marine substances, they are almost microscopic, and found only in the seas of hot countries. Inhabits the China seas. Three species. Creusia stromia. C. spinulosa. C. verruca. 6. Genus _Pyrgoma_. Pl. V. _Animal._ As above. _Shell._ Sessile, univalve, rather globular, ventricose, convex above; apex perforated; aperture small, elliptical, operculum quadrivalve. Inhabits the Indian seas. One species. Pyrgoma cancellata. 7. Genus _Anatifera_. Pl. V. _Animal._ Body covered with a shell, supported by a long tubular tendinous peduncle; with long, numerous, and unequal tentacular arms, which are articulated and ciliated, and emanating from the summit on one side. _Shell._ Compressed on the sides, with five flat valves, the valves contiguous and unequal; the lower lateral ones the largest: the whole of them united and kept together by means of their membranes. Inhabits the British seas. Six species. Anatifera lævis. A. villosa. A. vitrea. A. dentata. A. striata. A. aculeata. 8. Genus _Pollicipes_. Pl. V. _Animal._ Body covered by a shell, and supported on a tabular, tendinous, scaly peduncle; with many tentacular arms. _Shell._ Consisting of thirteen or more valves, the smallest at the sides, which are very flat and compressed, the peduncle short, wrinkled, rigid, and often covered with scales like shagreen. Inhabits the European and American seas. Six species. Pollicipes cornucopia. P. scalpellum. P. homii. P. mitella. P. peronii. · · · · · P. Mortoni.* 9. Genus _Cineras_. Pl. V. _Animal._ Body pedunculated, and encased in a membranous tunic, which is swollen above, with an opening below the summit, from which protrude many ciliated articulated arms. _Shell._ Composed of five testaceous oblong valves, two at the sides of the aperture and three on the back, not covering the whole of the body; supported by a peduncle of a greenish colour with several longitudinal stripes. Inhabits the British coast. One species. Cineras vittata. 10. Genus _Otion_. Pl. V.