Diagnosis. Shell oval, apex at or near posterior margin, coiled stage limited to protoconch; deck extending across full width of aperture, attached on both sides.
Remarks. Species are distinguished by position of the apex, whether at the margin or raised above it, and by the curvature of the edge of the deck and whether it projects forward at either edge. Subgenera are based on the form and position of the deck or septum, and are useful for the placement of fossil forms, although they were not utilized by Hoagland (1977). Applicable subgenera for this and the following genus are mentioned under the remarks for each species.

Animal with head depressed, laterally dilated, muzzle short, bilobed; tentacles short, subulate ; foot short, subtruncate in front, rounded behind.
Shell oval, patelliform, with a posterior generally lateral spiral apex ; interior with a basal plate covering the posterior half of the aperture.
Adhering to shells or stones, and modifying the form and surface in accordance with the inequalities of their place of attachment.
The distribution is world-wide ; the individual species have a wide range, which, added to their great variability, as in attached shells generally, has caused an enormous specific synonymy.
Fossil. — Cretaceous and Tertiary. In the Miocene the genus exhibits luxuriance both in size and variation.
Vernacular Name.—Slipper-limpet.