- Crepidula extinctorum.
- C. aculeata.
- C. lævigata.
- C. uguiformis.
- C. dilata.
- C. Peruviana.
- C. gigas.
- · · · · ·
- C. fornicata.*
- C. depressa.*
- C. glauca.*
- C. plana.*
- C. intorta.*
- C. convexa.*
7. Genus Ancylus. Pl. [X].
Animal. Body creeping, enveloped in the shell; two compressed subtruncated tentacular, with eyes situated at their internal base; foot short, elliptical; somewhat narrower than the body.
Shell. Thin, obliquely conical; aperture oval, with a pointed apex, which very much inclines backwards; margins simple. This is a fresh water shell, found in the lakes of Europe and rivers of America. Five species.
- Ancylus lacustris.
- A. fluviatilis.
- A. spinarosæ.
- · · · · ·
- A. rivularis.
- A. filosus.
FAMILY IV.
Bullacea. Three genera.
1. Genus Acera.
Animal. Body ovate, convex, transversely divided above into two parts; the foot with dilations in the form of wings below; head indistinct; branchiæ situated on the back, greatly behind, and covered by a mantle destitute of a shell. Inhabits the Mediterranean. One species.
- Acera carnosa.