This genus is evidently intermediary to the Paludina and the Natica. Its
species are probably all fluviatile; some attain a great size.
Shell thin, globular, ventricose; umbilicus small, forming a compressed
funnel-shaped aperture, without interior callosity; spire very short,
the last whorl much larger than all the others together; aperture ovate,
longer than broad, with margins united; right margin smooth and sharp;
columellar lip thickened, projecting, and reflected over the umbilicus;
operculum horny, rarely calcareous, thin, oval, not spiral, with
concentric elements; summit sub-marginal, inferior, passing obliquely by
the right edge of the aperture, but attached to the left.
Ampullaria Guyanensis.
A. rugosa.
A. fasciata.
A. canaliculata.
A. effusa.
A. Guinaica.
A. virens.
A. carinata.
A. avellana.
A. intorta.
A. fragilis.
_A. Guyanensis._ The Guiana Ampullaria.
Globular, thick, with unequal longitudinal striæ; covered with brown
epidermis; inside golden colour.
_A. rugosa._ The rough Ampullaria. Pl. 21, fig. 3.
Species dextral.
_A. Guinaica._ The Guinea Ampullaria.
Species sinistral.
_A. carinata._ The carinated Ampullaria.
Species sinistral, with a very large umbilicus, spirally carinated.
FAMILY XI.
NERITACEA. Five genera.