262 
The Mammals of Colorado 
genus, Elliot's Check-list giving thirty-five species and fifteen 
subspecies as found in North and Middle America, four of 
which have been met with in Colorado. 
Key of the Species 
A. Third unicuspid larger than fourth. Size small; tail about 
1.6; usually less. S. personatus, p. 262 
B. Third unicuspid smaller than fourth. 
a. Hind foot about 0.5. 
a'. Tail usually 1.75 or more; third unicuspid much smaller 
than fourth; ears inconspicuous; palate broad. 
S. obscurus, p. 264 
b'. Tail usually less than 1.75; palate narrow; ears larger; 
anterior part of rostrum attenuate. 
S. vagrans dobsoni, p. 264 
b. Hind foot decidedly less than 0.5; brain-case low, flat, and 
narrow. S. tenellus nanus, p. 265 
Sorex personatus (Lat. assumed, masked). Masked Shrew 
Sorex personatus Geoffroy Saint Hilaire, Mem. du Museum, 
Paris, XV., pp. 122-125 (1^27). 
Type locality. — Eastern United States. 
Measurements. — Total length, 3.8; tail vert., 1.6; hind foot, 0.46. 
Description. — Upper parts sepia brown, under parts ashy gray, 
tail bicolor, upper portion and tip similar to back, under portion 
lighter. Summer caught specimens are lighter and brighter in 
color than those taken in winter. 
The skull is small and rather slender, palate narrow and arched, 
anterior part of rostrum compressed and attenuate, unicuspids 
decreasing in size from first to fifth (viewed from the side they are 
sometimes in pairs, first and second subequal, and third and fourth 
subequal). The smaller size and the fact that the third unicuspid 
is larger than the fourth distinguish this species from 5. obscurus 
and dobsoni; and the latter characteristic and profile of skull 
sloping from rear to rostrum distinguish it from nanus. 
Distribution. — The Masked Shrew is found throughout the north- 
em part of North America from Alaska and the Arctic Region south 
to the Rocky Mountains of Colorado, the Cascade, and Sierra 
Nevadas. It is an inhabitant of the colder portions only, coming as 
low as the Transition Zone. In Colorado it is found through the 
mountains and seems to be fairly common. It has been reported 
from El Paso, Chaffee, Gunnison, Garfield, and Boulder counties. 
