creamy white; sides Ochraceous-Tawny, shaded in
the region of the shoulder with Cinnamon; rump and thighs
Cinnamon-Buff mixed with Smoke Gray; antipalmar surfaces of
forefeet Cinnamon-Buff; antiplantar surfaces of hind feet
Pinkish Buff; dorsal surface of tail Fuscous Black, overlaid
with Pinkish Buff; ventral surface of tail Ochraceous-Tawny,
Fuscous Black along margin, Pinkish Buff along outermost
edge; underparts creamy white. _Skull_: Large; braincase well
inflated; zygomatic arches strong and slightly appressed to
skull. _Baculum_: Large; long and slender.

_Comparisons._--From _E. q. hopiensis_, the only other
subspecies in this species, _E. q. quadrivittatus_ differs
in: Dorsal dark stripes blackish; crown grayer; rump and
thighs grayer; general tone of upper parts darker.

_Remarks._--Specimens from the Chuska Mountains, Zuni Mountains, and
Blanco, New Mexico, are intergrades between _E. q. quadrivittatus_ and
_E. q. hopiensis_, but are referable to _E. q. quadrivittatus_.

In north-central Colorado _E. umbrinus_ occurs in the spruce and pine
forests at higher altitudes, while to the south and east of this area
_E. q. quadrivittatus_ occurs in growths of pinon in lower, semiarid
areas. In the northern half of New Mexico and in south-central
Colorado, _E. q. quadrivittatus_ occurs not only in semiarid habitats
but also in the moist habitats of the forests of higher altitudes.
Ecologically, _E. umbrinus_ thus replaces _E. q. quadrivittatus_ in
north-central Colorado. This ecological replacement is comparable to
the ecological replacement of _Thomomys bottae_ by _T. talpoides_ in
Utah as shown by Durrant (1952:156).

_Specimens examined._--Total number, 130.

=Colorado=: _Larimer Co._: Arkins, 1 BS. _Jefferson Co._: W
spur Lookout Mountain, near Golden, 1 WC. _Gunnison Co._:
Sapinero, 3 BS. _Saguache Co._: 5 mi. N and 22 mi. W Saguache
10,000 ft., 1; 21 mi. W and 3 mi. N Saguache, 1. _Fremont
Co._: 18 mi. S and 7 mi. W Colorado Springs, 1; Arkansas
River, "about" 26 mi. below Canon City, 15 BS. _San Juan
Co._: Silverton, 1 BS. _Mineral Co._: 3 mi. E Creede, 1.
_Alamosa Co._: Sangre de Cristo Range, 24 mi. E Hooper, 2 CM.
_La Plata Co._: 2 mi. NE Bondad 6,100 ft., 1; Bondad, 15 mi.
S Durango 6,050 ft., 1. _Archuleta Co._: Chromo, 1 CM. _Las
Animas Co._: Trinidad, 6 BS. _Baca Co._: unspecified, 1.

=New Me