Type species. Cyclostrema bithynoides MONTEROSATO, 1880, Mediterranean. Etymology. Lissos - smooth, omphalos -umbilicus (Greek).
Diagnosis. Very small skeneiform archaeogastropods with strongly convex whorls sculptured with incremental lines only. Suture very deep. Umbilicus deep and wide, only with growth-lines. Protoconch with half a whorl and sculptured with 11 strong spiral ridges. Radula absent.
Remarks. Lissomphalia bithynoides is presently known only from shells, but a very similar, undescribed species from New Caledonia, of the same shape, sculpture, and number of same type of protoconch ridges, turned out not to have a radula. So did also a species from New Zealand (B. MARSHALL, pers. comm.). It is therefore presently impossible to classify this species in any known family. Pendromidae which family also lacks a radula, (see WAREN 1991) has a very different shell, not suggesting relationship.
Palazzia WAREN, 1991, which genus also seems to lack a radula, is presently classified in the Archaeogastropoda, but
the family position is uncertain. The shell does not suggest relations to Lissomphalia.
Although I have left the family position open, the genus can be placed in the Skeneidae, where it will easily be refound.