Yen 1954. Freshwater mollusks of Cretaceous age from Montana and Wyoming. Part 1. A fluviatile fauna from the Kooternai formation near Harlowton, Montana: Pap. 1-10. Part 2. An upper Cretaceous non-marine molluscan fauna from the Leeds Creek Area. Lincoln County, Professional Papers US Geological Survey, 233-A 1954: 1-20