C4G MONOGRAPHS OF NORTH AMERICAN ItODENTIA. 



hind and the British Provinces. Sciurus 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 Iowa, the lower parts are pale fulvous, varying in some specimens to 

 nearly white. In Southern Illinois, and at St. Louis, Mo., the color increases 

 to a strong bright fulvous, while in specimens from Lower Louisiana the 

 color is reddish-fulvous 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 

 Iowa, 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. Even 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.'' 



In 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 kudsonius group being the only instance 



