Animal. See Helix.
Shell. Found only in fresh water; subdiscoid or conoid, umbilicated, spiral, whorls, rounded; angular at the summit; aperture round, not modified by the penultimate whorl; the margins sharp and united; operculum orbicular and horny. Inhabits the rivers of Europe and America. Three species.
- Valvata piscinalis.
- · · · · ·
- V. arcnifera.* (Lea.)
- V. tricarinata.*
2. Genus Paludina. Pl. [X].
Animal. See Helix.
Shell. Generally found in fresh water, though some species have been found where it is salt; conoid covered with a greenish epidermis; the whorls rounded or convex, spiral cavity modified by the last whorl; aperture rounded, oval, oblong, angular at the summit; margins united, acute, never reflected outwards; operculum orbicular and horny. Inhabits the rivers of America and Europe. Thirty-one species.
- Paludina vivipara.
- P. Bengalensis.
- P. viridis.
- P. Francesii.
- P. achatina.
- P. Australis.
- P. impura.
- P. muriatica.
- · · · · ·
- P. sinistrosa.*
- P. Nuttaliana.*
- P. virens.*
- P. pallida.*
- P. subcarinata.*
- P. genicula.*
- P. magnifica.*
- P. limosa.*
- P. subglobosa.*
- P. lapidaria.*
- P. Virginica.*
- P. hyalina.*
- P. unicolor.*
- P. nuclea.*
- P. decisa.*
- P. fuscus.*
- P. dissimilis.*
- P. ponderosa.*
- P. integra.*
- P. porata.*
- P. lustrica.*
- P. grana.*
- P. Nickliniana.*
3. Genus Ampullaria. Pl. [X].
Animal. Inflated, globular, spiral; foot oval, with a transverse furrow at its anterior edge; head wide; tentacula superior, very long, conical, and pointed; eyes situated at their external base, and supported upon a very apparent peduncle; mouth vertical, situated between two lips disposed in form of a horse-shoe and forming a kind of muzzle; no superior tooth; a bristly lingual band, but not prolonged into the abdominal cavity; a very large respiratory cavity, divided in two by an incomplete horizontal partition.
Animals of this genus are oviparous; producing an egg nearly as large as that of a pigeon, in which is found the young animal complete, and in a perfectly formed shell.