Molluscs within this genus are characterized by elongated, wedge-shaped shells, distinguished from the genus
Pinna by the lack of any grooves in the
nacreous lining of the shell, and by the central positioning of the
adductor scar. As with other pen shells (
Pinnidae) they commonly stand point-first in the sea bottom in which they live, anchored by net of
byssus threads. ==Species==