Shell flat, inequivalve, inequilateral with the summits in anterior position; ears of unequal strength, the posterior one always larger or longer; sculpture made of fragile scales, becoming spiny in some species; inside nacreous with a well developed pallial margin in the colour of the outside.
 

Synonym Margarita Leach who describes it as follows: « Shell bivalve, unequal valved, winged, with one side gaping; wings unequal; hinge toothless; ligament internal, placed in a somewhat triangular excavation. Animal furnished with a byssus. » – W. E. Leach: The zoological miscellany vol.I, London 1814, p.107. The members of the genus have a long larval stage (16 to 30 days, according to Gervis & Sims: The biology and culture of pearl oysters (Bivalvia: Pteriidae) London 1992. The taxonomy of this group is not easy because shells do not bear marked specific features, especially at young stages.
 

« …bivalve, with long ears. One valve has a single tooth on the hinge, the other one bears a fovea that receives this tooth. » – J. A. Scopoli: Introductio ad historiam naturalem Praga 1777, p.397.