"Noah's Ark Shell." Oblong, oval, or subquadrate; surface covered by a rude, caducous periostraeum; hinge line straight or slightly curved; teeth numerous, the central ones smaller, the lateral ones becoming gradually larger and more oblique towards the extremities; ligament external, inserted upon a narrow surface between the approaching umbos; pallial line entire. The species belonging to this genus have a byssus as distinct from those of true Arca.
Distribution: Cosmopolitan. Type species: Arca barbata Linne 1758.