amined from
Montana, South Dakota, and Wyoming I concur with Anderson. Bailey's
characterization of _wahema_ is applicable to _insperatus_ as I
interpret it. In the Black Hills, _Microtus longicaudus longicaudus_
(Merriam) occurs together with _insperatus_.

_Specimens examined._--Total 123. _Wyoming_: SHERIDAN CO.: 3 mi.
WNW Monarch (=Kleeburn), 3800 ft., 4; 4 mi. NNE Banner, 4100 ft.,
26; 5 mi. NE Clearmont, 3900 ft., 3. JOHNSON CO.: 5-1/2 mi. W, 1
mi. S Buffalo, 5520 ft., 1; _5-1/2 mi. W, 1-1/2 mi. S Buffalo_, 1;
_1 mi. W, 4/5 mi. S Buffalo_, 4800 ft., 36; 1/4 mi. E Klondike,
5160 ft., 1. CAMPBELL CO.: Belle Fourche River, 45 mi. S, 13 mi. W
Gillette, 5350 ft., 2. CROOK CO.: 3 mi. S, 2 mi. E Rocky Point,
3800 ft., 6; Bear Lodge Mts., 6-1/2 mi. SSE Alva, 1 (Mich); _15 mi.
N Sundance_, 5500 ft., 3; 15 mi. ENE Sundance, 3825 ft., 6; _3 mi.
NW Sundance_, 5900 ft., 1; _1-1/3 mi. NW Sundance_, 5000 ft., 4;
Sundance, 1 (USBS). WESTON CO.: 1-1/2 mi. E Buckhorn, 6150 ft., 26;
Newcastle, 1 (USBS).

GENERAL REMARKS

The region considered in this paper differs in several regards from the
state of Pennsylvania, where variation in the skulls of this species
has been studied in detail by Snyder (1954) who referred all
populations there to a single subspecies. In some characteristics of
the skulls, populations within Pennsylvania differed as much or more
than the subspecies from Wyoming and Colorado. In other characteristics
of the skulls and of the skins differences are greater between
populations in Wyoming and Colorado. The region discussed here is
approximately five times as large as the state of Pennsylvania.
Populations of _M. pennsylvanicus_ are less continuously distributed
than in Pennsylvania owing to major physiographic and climatic barriers
and also owing to competition with one or more of the five other
species of _Microtus_ occurring in this region. The distribution of
three of these species has been discussed by Findley (1945:419). Large
areas of relatively greater aridity, such as the region occupied by the
subspecies _insperatus_, occur in Wyoming and Colorado. I have pointed
out that the populations which I have designated as subspecies are not
absolutely uniform. Also the different subspecies are not of exactly
equal degrees of difference. However, there is considerable uniformity
of populations occupying conveniently mapped geographic areas. In my
opinion, the