On the basis of large collections from the Montoya Group of western Texas, the Maquoketa Shale of Iowa and Minnesota, and the Richmond Group of Ohio and Indiana (all Ordovician), definitions of these three brachiopod genera are emended to permit morphologic overlap. All have well developed teeth located near the lateral edge of the hinge line, elongate sockets, triangular hinge plates, high blade-like cardinal processes, and flabellate ventral muscle patterns. The value of dental plates for generic discrimination among these three genera is questioned; the cruralium is variable; the strength of the fold, and the lateral outline are useful only on the specific level.

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