Abstract

Orthacea in the Upham, Aleman, and Cutter formations include Glyptorthis insulpta maquoketensis Ladd, Hesperorthis kirki n. sp., Plaesiomys bellistriatus Wang, P. cf. P. subquadratus (Hall), P. subquadratus cutterensis n. subsp., Hebertella occidentalis montoyensis n. subsp., Austinella kankakensis (McChesney), Platystrophia prayi n. sp., and an unnamed species of Platystrophia. Comparison of muscle scar patterns in Plaesiomys shows difficulty of basing specific differentiation upon pedicle valve musculature; number of costae per unit distance along the anterior margin, when correlated with shell size, proves to be more reliable. The Aleman and Cutter are correlated with the Maquoketa Shale of Iowa (Cincinnatian).

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