The shell is minute, Neritoid or Crepidula-like, with a small
depressed lateral spire, apparently dextral, composed of about 1
very rapidly enlarging whorls, the last very convex dorsally,
imperforate; the apex is smooth, and the last whorl is spirally striate.
The aperture is very large, oblique, transversely oval, the peristome
continuous and free, thin. Carity of the spire very small, a thin,
broad, concave columellar plate projecting across the end next the
spire, as in Crepidula or Latia.
The soft parts are sinistral, externally Limnaeoid, with large
black eyes near the inner bases of the short blunt cylindric tentacles.
Two adductor muscles, kidney-shaped in section, one on each side,
replace the usual columellar muscle.
The radula has 18, 1, 18 teeth, arranged about as in Lymnaea.
Centrals with a single cusp, the laterals bicuspid, the outer cusp
smaller. The transition teeth have four or five cusps. The marginal
teeth are low, wide and separated, with four or five cusps.
There is a short false gill hanging in the pallial cavity.
The shell has some resemblance to Crepidula and Latia. Lepyrium
and Pompholyx are also slightly similar; but the resemblance
is no doubt superficial. Pompholyx, like Amphigyra, is sinistral
with an ultrasinistral shell. It has no plate or lamina across the
visceral cavity. The soft anatomy of Amphigyra, so far as worked
out, seems to show most affinity with the Ancylidae.
The deck of Amphigyra is present at all stages of growth observed,
in young as well as mature shells. In Gundlachia no septum
is developed until a period of hybernation or aestivation is reached.
The shell is more solid than that of Ancylus or Gundlachia.
