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.