646 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
land and the British Provinces. Sciwrus carolinensis is perhaps a still more 
marked example, in which the color varies from the light pure gray of the 
upper parts in New England specimens, with a restricted pale yellowish- 
brown dorsal area, to the rusty-gray dorsal surface of the Florida type, in 
which the whole upper surface is usually strongly yellowish-rusty. This 
increase of color southward is, however, still more strongly marked in the 
Fox Squirrels of the Mississippi Basin—the so-called Sciurus ‘ludovicianus’. 
In specimens from Ohio, Northern Illinois, Southern Michigan, Wisconsin, 
and Towa, the lower parts are pale fulvous, varying in some specimens to 
nearly white. In Southern Illinois, and at St. Louis, Mo., the color increases 
toa strong bright fulvous, while in specimens from Lower Louisiana the 
color is reddish-fulvuus or deep orange. At the same time, the color of the 
dorsal surface becomes proportionally darker at the southward, through the 
greater breadth of the black annulations at the tips of the hairs, the dorsal 
surface in Louisiana specimens being many shades darker than in those from 
the Upper Mississippi. This variety also finely illustrates the variation in 
color seen in specimens from comparatively dry and moist regions, its habitat 
extending up the Missouri and its western tributaries to a point considerably 
above Sioux City. Beginning with Ohio specimens and passing westward, 
we find an increase of color in those from Northern Illinois, Wisconsin, and 
Towa, west of which point the color rapidly decreases in intensity, Nebraska 
[and Dakota] specimens being much paler than those taken on the same 
parallel near the Mississippi River. Specimens from the Indian Territory 
are also very much paler than those from St. Louis, as are Texas ones than 
those from Louisiana. Eyen between specimens from the prairies of North- 
western Louisiana and others from the lowlands of the same State, near the 
Mississippi River, the difference in color is very strikingly marked.” 
Jn addition to the variation in color with latitude referred to above, there 
is, as is now well known, an equally well marked, if not even still greater, 
variation in color between representatives of the same species in respect to 
longitude, in not only the Squirrels, but among both Mammals and Birds that 
range across the continent. In respect to this variation in the Squirrels, I 
have already spoken, in the above-cited paper, substantially as follows :— 
“But few specific forms, however, have a sufficiently wide range to 
illustrate the variations that obtain along a given parallel across the whole 
breadth of the continent, the Sciurus hudsonius group being the only instance 
