_fasciatus_. This impelled me to examine material
from the entire range of _P. fasciatus_. This examination revealed that:
(1) _Perognathus callistus_ Osgood, heretofore considered to be a full
species, should be reduced to subspecific rank under _P. fasciatus_; and
(2) specimens from eastern Wyoming and adjacent parts of Montana, South
Dakota and Nebraska represent an heretofore unrecognized subspecies.
Further investigation, however, revealed that _Perognathus flavescens
olivaceogriseus_ Swenk, described from northwestern Nebraska (Swenk,
1940:6), is not _flavescens_ but actually _fasciatus_. Since the
specimens on which Swenk's description was based were taken within the
range of this newly recognized subspecies, and since my examination of
the holotype shows it to be of the species _Perognathus fasciatus_, the
subspecific name _olivaceogriseus_ is available.

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 Sta