Crassatella evensi from the Pierre Shale of Custer County South Dakota (AMNH 66246). Image modified from fig. 39e in Landman et al. (2010, Bulletin of the American Museum of Natural History, no. 342) and used with permission. Nympholucina occidentalis from the Maastrichtian Fox Hills Fm. of Dewey County, South Dakota (YPM 024427).
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