_M.
pennsylvanicus_ has been taken at scattered localities. This scattered
and localized distribution of suitable habitat undoubtedly limits
gene-flow between these relict populations. Presumably as a result of
this isolation _finitus_ has accumulated and maintained its distinctive
characteristics. The subspecies is so named because of its limited
range. The average weight of eight specimens (4 males and 4
non-pregnant females) from Dundy County is 57.2 grams.

_Specimens examined._--Total 26. _Colorado_: YUMA CO.: Wray, 3
(USBS); _1 mi. W Laird_, 2. _Nebraska_: DUNDY CO.: 5 mi. N, 2 mi. W
Parks (Rock Creek State Fish Hatchery), 19; Haigler, 2 (USBS).

Microtus pennsylvanicus pullatus new subspecies

_Type._--Adult male, skin and skull, number 37873, University of
Kansas, Museum of Natural History, obtained by Rollin H. Baker,
original number 1343, 12 miles north and 2 miles east of Sage, 6100
ft., in Lincoln County, Wyoming, on July 19, 1950.

_Range._--North-central Utah, eastern Idaho, western Wyoming, and
southwestern Montana. See Figures 1 and 2.

_Diagnosis._--Size average; color dark, especially in southern part
of range; tail relatively long; molar teeth small; nasals
relatively broad; maxillary septum relatively small.

_Comparisons._--From _M. p. uligocola_, the subspecies to the
southeast, _M. p. pullatus_ differs as follows: relatively darker
in southern part of its range (see Figure 1); smaller, tail
relatively longer. In 6 of 7 pairs of skulls compared of _pullatus_
(from Lincoln Co., Wyoming) and _uligocola_ (from Larimer Co.,
Colorado), _pullatus_ had relatively broader nasals (Confidence
Limit .85); _uligocola_ had larger maxillary septa (C. L. .97) and
larger molar teeth (C. L. .90). From _insperatus_, the subspecies
to the east, _pullatus_ differs as follows: both summer and winter
pelage darker; tail longer both actually and relatively; upper
molar tooth-row shorter. Ten pairs of skulls of specimens from near
Afton, Wyoming, representing _pullatus_, and from northeastern
Wyoming, representing _insperatus_, revealed no significant
differences in the features observed by the "method of pairs".
Although not compared in detail with the subspecies to the north,
_M. p. drummondi_ (Audubon and Bachman), examination of specimens
from western Montana and the accounts of other authors in