There are 80 or more living specis of helmet shell. They usually have a short spire and a columinous body whorl which may be ornamented with knobs, ribs, or varices. The outer lip is thickened, often toothed and, in some larger species, greatly expanded; the columella may differ from female shells. The animals are sand dwellers, feeding mostly on sea urchins; they have a small, thin and corneous operculum.