Geologic setting and the family Pupillidae (Pulmonata: Stylommatophora)

A large, diverse, and well-preserved fauna of nonmarine mollusks has been recovered from the late Oligocene to early Miocene (Arikareean) fluviatile and lacustrine sediments that accumulated in four intermontane structural basins of western Montana. The Pupillidae are represented by 10 species, with nine new species and one new subgenus among three extant genera. The Gastrocopta are very diverse, with one new subgenus Ameralbinula represented by three new species, G. obesa, G. russelli, and G. oviforma, while three new species, G. tavennerensis, G. leonardi, and G. Conica are referred to the extant subgenus Vertigopsis Sterki, 1893. Gastrocopta miniscula cannot be referred to a subgenus with certainty. The remaining new species, Vertigo whitei and Pupoides montana, are referred confidently to extant subgenera. Vertigo arenula (White, 1876) is the only previously described species and its description is emended based on new material. The mammalian biostratigraphy of the Cabbage Patch beds is presented.