404 U. S. P. R. R. EXP. AND SURVEYS—ZOOLOGY-GENERAL REPORT. 
character of this animal, it is in this way readily distinguishable from any other described 
species of Thomomys. The fore foot is said to have a rudimentary thumb; the middle toe 
longest, the first and third equal, (second and fourth ?) the outer one is shorter and far back, 
the thumb still further back. The rudimentary fifth toe is so small as to be scarcely discernible. 
The cheek pouches are covered on the outside with hair of the same color as that on the 
back ; but beneath and on their posterior margins their color is white. On the head and body 
the fur is of a grayish black color, with a faint brownish reflection in some lights ; it is as fine 
as that of the mole, but not so velvety. Chin and throat white. The tail is very short and 
cylindrical, and covered by a close smooth coat of short white hairs. 
Inches. 
Length of head and hody.... 
7.00 
tail _ . _____.....-......... 
1. 84 
'N’osft to p.yo_ T ,___,___ 
. 75 
ear. _ _____ 
1. 25 
Fore foot___...................___.... 
. 90 
Middle fore claw........................... ........._ 
.33 
Hind foot _ _,_ 
.92 
The specimen described was obtained from Hudson’s Bay, and is now in the museum of the 
Zoological Society. 
