Formal names, diagnoses, and descriptions are supplied for previously identified, but informally named, cryptodiran turtles from the Paleogene of Montana and Wyoming, USA. Two new early Paleocene (Puercan) turtles are described from Montana: a peculiar trionychid, Atoposemys entopteros gen. et. sp. nov., from the Tullock Member of the Fort Union Formation, and a chelydrid, Tullochelys montanus gen. et. sp. nov., from both the Tullock Member of the Fort Union Formation and the Hell Creek Formation. From the Wasatchian (early Eocene) Wasatch and Willwood formations of Wyoming, the following taxa are described: the earliest North American emydid, Psilosemys wyomingensis gen. et. sp. nov.; a platysternid, Cardichelyon rogerwoodi gen. et. sp. nov.; and Planetochelys dithyros sp. nov. A new family, Planetochelyidae, within the Trionychoidae, is erected for Planetochelys.