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.