Praecardiidae.-Shell equivalve with hinge dentition as in Arca.
Cardiolidae.-Shell equivalve and ventricose; hinge without teeth.
Grammysiidae.-Shell thin, equivalve, oval or elongate; hinge without teeth.
Solenopsidae.-Shell equivalve, greatly elongated, umbones very far forward.
Cyrtodontidae.-Extinct; shell equivalve and inequilateral, short, convex.
Shell equivalve, with an external ligament.
Shell equivalve, with radiating costae and external ligament.
The word usage examples above have been gathered from various sources to reflect current and historial usage. They do not represent the opinions of YourDictionary.com.