(1917) in his
description of _caryi_ made four assumptions that have been found to be
entirely or partly invalid. First, he assumed that this is an "extreme
variant which gradually changes in characters across Nevada and Utah,
and reaches its maximum variation in Wyoming." The differences pointed
out in subsequent descriptions of subspecies found in the above area do
not show a gradual change in any character, or in the number of
characters, nor is _caryi_ an extreme when compared with the other
subspecies. Second, _Microtus nanus_ was not, as Bailey assumed, a
different species than _Microtus montanus_. Third, he assumed that the
characteristics of adults of _nanus_ were adequately ascertainable from
the thirteen topotypes available to him. Subsequent sampling from Idaho
shows that the series of specimens available to Bailey was made up
mostly of young and subadult animals. Finally, _caryi_ does not occupy
as Bailey stated "the meadows along streams in the arid sagebrush
country of the Bear River, Green River, and Wind River valleys"
exclusively, or characteristically. When the localities from which the
species actually is known are plotted, it seems that the arid basin
serves as a barrier and that the species is more commonly and abundantly
found in montane meadows in the Transition and Canadian life-zones.

Certain samples, here assigned to _M. m. nanus_, that vary from the
average of the subspecies deserve comment. For example, mice from the
area in Wyoming southwest of the Green River (in the Uinta Mountains)
have relatively smaller feet, but are larger in both total length and
size of skull. Specimens from near Afton, Lincoln County, Wyoming, are
relatively large in both total length and size of skull. This series and
specimens from Teton County, Wyoming, are intermediate between _nanus_
from Idaho and the newly named subspecies from near Cody, Park County,
Wyoming, described below, in terms of both darkness and the amount of
reddish color. Mice from Laramie County are more richly reddish-brown.
The specimens from near Savery, in Carbon County, Wyoming, are darker.
The alveolobasilar length relative to the condylobasilar length is
smaller in the series from along Deer Creek, 16 mi. S, 11 mi. W Waltman,
Natrona County, Wyoming. The series from the southern tier of counties
in Wyoming and some of the specimens from Colorado have relatively wider
zygomatic arches. The specimens from southern Sweetwater County,
Wyomi