t of increased understanding of these mice
through additional collecting are expressed in the synonymies under the
accounts of subspecies. As a result of my studies two of the three
subspecific names previously proposed for mice from this area have been
retained although changes are proposed in the ranges assigned to the two
subspecies and two additional heretofore unrecognized subspecies are
named and described. Furthermore the additional specimens and my studies
of variation make modifications in the characterization of these
subspecies necessary. Not all of the samples here assigned to a single
subspecies are identical and I therefore list and discuss some of the
local variants.

Numerous members of summer field parties from the Museum of Natural
History at the University of Kansas collected most of the specimens
studied and wrote field notes that have been helpful. I am grateful
to these persons and to Professor E. R. Hall and Dr. R. H. Baker
for their assistance and helpful suggestions. Specimens in the
following museums were made available by their respective curators:
Chicago Natural History Museum by Mr. Colin C. Sandborn, The Museum
of Zoology at the University of Michigan by Dr. E. T. Hooper, The
American Museum of Natural History by Mr. G. G. Goodwin, The United
States National Museum by Dr. David H. Johnson and the Biological
Surveys Collection by Miss Viola S. Schantz. A fellowship from the
National Science Foundation made possible the studies at the
museums other than at the University of Kansas.

=Microtus montanus nanus= (Merriam)

_Arvicola (Mynomes) nanus_ Merriam, N. Amer. Fauna, 5:62, July 30,
1891.

_Microtus montanus nanus_, Hall, Proc. Biol. Soc. Washington,
51:131, August 23, 1938.

_Microtus nanus_, Bailey, N. Amer. Fauna, 17:30, June 6, 1900
(part).

_Microtus montanus caryi_ Bailey, Proc. Biol. Soc. Washington,
30:29, February 21, 1917.

_Microtus nanus nanus_, Cary, N. Amer. Fauna, 42:43, October 3,
1917 (part).

_Type._--Adult male No. 23853/31253, U. S. National Museum,
Department of Agriculture collection, from Pahsimeroi Mountains,
Custer County, Idaho; obtained by C. Hart Merriam and Vernon
Bailey, September 16, 1890.

_Range._--Idaho; southwestern Montana; most of the southwestern
half of Wyoming; southward to central Colorado.