Pierce, H.G.; Rasmussen, D.L. (1992). The nonmarine mollusks of the Late Oligocene-Early Miocene Cabbage Patch fauna of western Montana. I. Geologic setting and the family Pupillidae (Pulmonata: Stylommatophora). Journal of Paleontology. 66(1): 39-52.
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Pierce, H.G.; Rasmussen, D.L.
1992
The nonmarine mollusks of the Late Oligocene-Early Miocene Cabbage Patch fauna of western Montana. I. Geologic setting and the family Pupillidae (Pulmonata: Stylommatophora)