The author served in the Rocky Mountain Herbarium of the University of Wyoming as personal research assistant to Dr. Aven Nelson during the years 19291930. It was his good fortune to have an opportunity to study the specimens of ferns in the Rocky Mountain Herbarium and to review class notes from a number of lectures delivered by the late Dr. Edwin B. Payson. The key to the ferns as adapted to this paper was originally worked out by Elias Nelson. Dr. Payson made a number of changes. Many of the notes upon the several genera as well as numerous citations represent the work of Dr. E. B. Payson. (Herbarium numbers allude to specimens of the Rocky Mountain Herbarium.)