The subspecies of _P. fasciatus_ are most easily distinguished by color of pelage, in which there is a general cline from northeast (dark) to southwest (pale). Cranially, the subspecies are less distinct. The skulls of _P. f. callistus_ can be distinguished from those of the other subspecies by several differences; however, among the other four subspecies, only minor cranial differences are evident. Individual variation was found to be greater than secondary sexual variation. [Illustration: FIG. 1. Distribution of the five subspecies of _Perognathus fasciatus_. Solid symbols represent specimens examined; circled symbols represent type localities. Guide to subspecies 1. _P. f. fasciatus_ 2. _P. f. olivaceogriseus_ 3. _P. f. infraluteus_ 4. _P. f. litus_ 5. _P. f. callistus_ ] In connection with this study, grateful acknowledgment is made to the following persons for the loan of specimens in their care: Dr. H. E. Anthony, American Museum of Natural History (AMNH); Mr. Colin C. Sanborn, Chicago Natural History Museum (CNHM); Mr. Austin W. Cameron, National Museum of Canada (NMC); Miss Viola S. Schantz, Biological Surveys Collection, U. S. National Museum (USBS); Dr. Seth B. Benson, University of California Museum of Vertebrate Zoology (MVZ); Mr. J. E. Moore, Department of Zoology, University of Alberta (UADZ); Dr. William H. Burt, University of Michigan Museum of Zoology (MZ); Dr. Otis Wade, University of Nebraska Department of Zoology (UNDZ); Dr. C. Bertrand Schultz, University of Nebraska State Museum (NSM); and to those in charge of the collections of the Nebraska Game, Forestation and Parks Commission (NGFPC). Specimens from the Museum of Natural History, University of Kansas (KU), also have been used. Capitalized color terms are those of Ridgway, Color Standards and Color Nomenclature, Washington, D. C., 1912. Assistance with field work to obtain specimens for the University of Kansas Museum of Natural History is acknowledged from the Kansas University Endowment Association and the National Science Foundation. =Perognathus fasciatus fasciatus= Wied-Neuwied _Perognathus fasciatus_ Wied-Neuwied, Nova Acta Phys.-Med. Acad. Caesar. Leop.-Carol., 19:369, 1839, type from Upper Missouri River near its junction with the Yellowstone, near Buford, Williams County, North Dakota. _Geographic distribution._--Southwestern Manitoba, extreme northeastern Montana and all of North Dakota except extreme eastern part, south through central South Dakota to the northeastern part of Cherry County, Nebraska (see Figure 1). _Remarks._--For comparisons with _Perognathus fasciatus olivaceogriseus_, geographically adjacent to the southwest, see account of that subspecies.