The name Baculites asperiformis Meek has been applied in a very broad sense to early Montana (Campanian) baculites that have ribbed venters, ribbed or noded flanks, and moderately complex sutures. The species is herein restricted in its scope, and 2 forms formerly included in it are described as the new species B. gilberti and B. perplexus. The sequence of baculites in the Sharon Springs Member and the Mitten Member of the lower part of the Pierre Shale [Cretaceous] and in the equivalent rocks of the Western Interior seems to be, from oldest to youngest, B. obtusus Meek, B. maclearni Landes, B. asperiformis Meek and B. perplexus, n. sp. Locally a smooth unnamed species marks a thin zone just above that of B. asperiformis The new species A. gilberti lies within the Zone of B. perplexus s.l.

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