The shell has a trochoidal shape. It is nacreous within. It is umbilicate or imperforate, having a deep slit or sinus in the outer superior margin of the peristome, which serves the purpose of an
exhalant phase of
respiration., and leaves on the corresponding part of the
whorls a peculiarly sculptured band, the "anal fasciole" or the "slit fasciole." The slit is sealed up gradually behind the advancing aperture as the shells grows in size. The animal has no frontal lobes or appendages. The eyes are situated at the outer bases of the tentacles. The muzzle is as in
Trochidae. The tentacles are long, subcylindrical and bluntly pointed. The broad epipodium (the lateral grooves between foot and mantle) is thin, entire, and fringed with a row of small, short papillae. But it does bear cirri. It is closely applied to the shell. The long
radula has a long, narrow rhachidian tooth. It is lanceolate with its tip narrowand recurved. There are 26 laterals with the outer 5 without cusps. The inner ones are larger, with wide cusps and narrower bases. The outside of the laterals consists of 2 rows of uncini (the numerous small teeth-like or hook-like structures). The inner series number 18 and are large, strongly curved, and with scythe-shaped 1-3 denticulate cusps. The outer uncini are very numerous (40-50), small, very oblique. In
Entemnotrochus adansonianus (Crosse & P. Fischer, 1861) there are considerable differences in the teeth. Some of the uncini bear little tufts of bristles at their apices. The jaws are subobsolete. ==Fossil record==