The shell is highly variable in sculpture. It is rather small, the aperture
is wide and strongly inflated, about 50 percent of shell length. The keel is wide and
bears the characteristic 15 to 20 prominent large and blunt nodules placed in pairs
over the keel. Great variations exist in size and form of the nodules. The ribs on the
sides of the shell extending from the cranial knobs are less numerous than in the
other species, with less bifurcation. There are two types of ribs present: 11–13 long
and full sized ribs extending from the nodules to the nucleus which are in regular
alternating series with the secondary ones; the latter 10–12 are short and extend up
to halfway from the nodules. The color of the shells varies from white with brownish
black tint on the nodules and adjacent ribs to light brown with sooty brown pigmentation
over most of the surface of the shell