Shell very oblique, wedge-shaped, triangular, equivalve, exceedingly inequilateral, more or less thin and fragile, gaping posteriorly; surface smooth or scaly, or obliquely furrowed; hinge line long; umbos terminal; valves carinate.
Distribution: Cosmopolitan.
Remarks: Aristotle was the first author to mention Pinna. Synonyms are: Pinnarius Dumeril 1806, Pinnula Rafinesque 1815, Chmaera Poli 1791.