(U. S. N. M.).

_Additional records._--Bailey (N. Amer. Fauna, 39:101, 112, November 15,
1915) has recorded the following specimens, which on geographic grounds,
would presumably be referable to _Thomomys talpoides rostralis._
COLORADO: Estes Park (referred by Bailey, p. 101, to _T. t. clusius_),
1; Colorado City, 1; Colorado Springs, 2-1/2 mi. N, 6000 ft., 1;
Colorado Springs, east of Palmer Park, 1; Montgomery, 3; Nederland, 4;
Teller County Divide, 1. These specimens have not been examined by us.

=Thomomys talpoides attenuatus= new subspecies

_Type._--Male, adult, skull and skin, no. 15095 Mus. Nat. Hist., Univ.
Kansas; from 3-1/2 mi. W Horse Creek Post Office, 7000 ft., Laramie
County, Wyoming; obtained on July 16, 1945, by Henry W. Setzer; original
no. 629.

_Range._--Southeastern Wyoming from Niobrara County south into Weld
County, Colorado.

_Diagnosis._--Size small; color pale (whitish); skull smooth and,
relative to its length, slender; rostrum relatively long; nasals
truncate posteriorly; middle parts of zygomatic arches straight;
temporal ridges low and more widely separated in middle extent than at
anterior or posterior ends; tympanic bullae rounded and moderately
inflated; interpterygoid space V-shaped.

_Comparisons._--From _Thomomys talpoides bullatus_ (topotypes) to the
northward, _T. t. attenuatus_ differs in smaller size, lighter (less
brownish, more whitish) color, smaller and slenderer skull. In detail,
some cranial features diagnostic of _attenuatus,_ when compared with
_bullatus,_ are: Anterolateral angle of zygoma less nearly a right
angle; temporal ridges bowed outward at middle, instead of straight, and
farther apart posteriorly than anteriorly instead of nearly parallel;
sides of basioccipital nearly straight instead of concave.

From _Thomomys talpoides cheyennensis_ (holotype and Wyoming specimens
from: Pine Bluff; 1 mi. W Pine Bluffs, 5000 ft.; 12 mi. N and 1/2 mi. W
Pine Bluffs) to the eastward, _T. t. attenuatus_ differs in smaller size
throughout and more slender skull. The two subspecies are
indistinguishable in color.

From _Thomomys talpoides macrotis_ (topotypes) to the southward, _T. t.
attenuatus_ differs in smaller size, slightly lighter (less brownish and
more whitish) color, smaller and slenderer skull.

From _Thomomys talpoides rostralis_ (specimens from the type locality)
to the westward, _T. t. attenuatus_ differs in smaller size; lighter
(grayer, less brownish)