Shell is black or purple above and white below, coiled, with a
definite raised spire (but the shell is only about as tall as
wide), no siphonal notch or canal in aperture, interior of the
shell is pearly. Animal has an operculum which is thin and horny
with spiral lines. Columella has two small nodes. The umbilicus
is closed by a callus (picture). Shell up to 3 cm diameter. The
apex is frequently heavily worn, and shell may be encrusted with
coralline algae or bryozoans. Animal's foot is black on the
sides. The black on the shell is due to a dark periostracum.