They have medium-sized thick aragonite shells which are almost circular. The surface is either smooth or radially ribbed. The hinge is heavy, with a row of 6-12 teeth. The shells are generally biconvex, with equal valves round in outline, and slightly longer than wide. Their size varies from medium to large. The external hinge ligament lacks transverse striations.
They burrow into the sand and mud in shallow saltwater beds. Facultatively mobile. Infaunal suspension feeders. They prefer beds with heterogeneous-grained sediments.
They evolved convergently with genus Composita.
These clams are very common as fossils. Fossil shells of these molluscs can be found all over the world. Today, they are common in North Carolina.
This genus was named by da Costa in 1778.