332 U. Ss. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
dark plumbeous at the extreme base, then very pale cinnamon, then reddish brown as described ; 
the latter of greatest extent. There is considerable difference, however, in different specimens 
as to the amount of the pale color at the base of the hairs; in some this being displaced by the 
reddish brown. The hairs beneath are brownish at the base posteriorly ; anteriorly they are 
generally uniform pale brownish yellow throughout. The whiskers and edges of the eyelids 
are black ; the iris is also black. The tail generally is colored like the back ; for one-third or 
one-half from the tip it is black; the hairs being reddish white at the base, and some of them 
tipped with the same. 
In examining a large series of prairie dogs collected at different seasons, it will be seen that, 
as a general rule, they are much brighter colored in summer, in some cases of a bright rusty or 
brick red ; the tips of the hairs lighter. These tints become paler towards the winter, fading in 
a measure to a grizzled yellowish gray and dull light brown. The fur becomes fuller and softer 
in every way. In summer the sole is generally naked, except an isolated patch of greater or 
less extent in the centre ; in winter this patch increases in size, though generally separated by 
a narrow line from the hairs on the sides of the feet and on the heel. 
In winter specimens the under fur is very dark sooty plumbeous, then pale yellowish or cin- 
namon white for most of its extent, and tipped with various shades of reddish brown. In all 
cases the under parts are much lighter than the upper ; sometimes they are of a brownish silver 
gray, sometimes with a tinge of yellowish rusty, either continuously or in patches. 
From the accompanying list of localities it will be seen that the prairie dog has a very exten- 
sive distribution, being found over the entire extent of the region between the Missouri River 
and the Rocky Mountains. It has not been hitherto recorded as occurring north of the United 
States line, as Richardson does not mention it as an inhabitant of the Saskatchewan. Southward 
it extends to the Rio Grande, certainly as far as the vicinity of Presidio del Norte, in latitude 
30°; it is probable, however, that it does not reach as far south on the river as Matamoras, as 
Dr. Berlandier does not mention it in his notes on the zoology of that region. 
