2. Physa. Four species.
This genus is generally heterostrophe (that is, with whorls turned to the left hand); found in fresh water; it greatly resembles the Lymnæa, but has not a widened aperture.
Shell often sinistral, oval, oblong, or globular, perfectly smooth; aperture oval, contracted posteriorly; the right edge sharp, advanced above the plane of the left edge; columella twisting obliquely, and enlarging to join itself to the anterior part of the columellar margin.
Physa castanea.
P. fontinalis.
P. hypnorum.
P. subopaca.
P. fontinalis. The fountain Physa. Pl. [20], fig. 2.
Volutions reversed, oval, ventricose, pellucid, horn-coloured; spire short and acute.