Leptaena

Leptaena is an extinct genus of mid-sized brachiopod that existes from the Dariwilian epoch to the Emsian epoch, though some specimens have been found in strata as late in age as the Tournasian epoch. Like some other Strophomenids, "Lepteana" were epifaunal, meaning they lived on top of the seafloor, not buried within it, and were suspension feeders. 
Physical description.
"Leptaena" usually have concentric wrinkling and concentric lines on the shell. "Leptaena" have a concavo-convex profile, and are sometimes Semiquadrate to semielliptical. The Cardinal Process is split in two and the hinge line is straight. Their width is usually greater than their length, like most Strophomenids.
Distribution.
"Leptaena" fossils have been found on every continent except Antarctica. 
Species.
"Leptaena" was a diverse genus, with over 70 recognized species and subgenera. Species in the genus "Leptaena" include the following. Any synonymous genera to which a given species may belong to are labelled with the synonymous genus in parentheses.