Rostrate articulated brachiopods with biconvex shell that usually has dorsal fold and ventral sulcus; interareas typically low and limited to ventral valve. Shell commonly with coarse costae, sometimes fine; mostly impunctate. Ventral interior typically with dental plates; spondylium normally absent. Dorsal interior commonly with medium septum supporting septalium or hinge plates; outer parts of hinge plates form bases for crura that in recent genera are attached to spirolophous lophophore. Lower Ordovician (Llanvirn)-Holocene.
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