Middle Devonian fishes from the Lemhi Range of Idaho

The basal unit of the Jefferson formation at the head of Spring Mountain Canyon, Lemhi County, Idaho contains the following fishes: a heterostracan, Psephaspis idahoensis n.sp., which is shown to belong to the Pteraspididae rather than the Drepanaspididae; the arthrodire, Holonema haiti n.sp., and undetermined arthrodires; an antiarch referred to the Astrolepididae indet.; and a spine possibly belonging to a holcephalian. The age is considered to be Middle Devonian, and the depositional environment possibly estuarine.