Leptodus, extinct genus of articulate brachiopods, or lamp shells, of the Permian Period (299 million to 251 million years ago). Leptodus, a very specialized form characterized by an aberrant morphology, had an oysterlike pedicle valve, which anchored the shell to the substrate and was probably attached to other shells by cementation. The brachial (upper) valve was flat and very thin. It is likely that Leptodus inhabited the flanks of reefs developed in shallow Permian seas of North America.