G76 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



the toes being naked. The general pelage is also much fuller, longer, and 

 softer in winter than in summer. 



The skull presents the usual range of individual variation so often noted 

 in these papers, especially in respect to the form of the nasal bones. These 

 van - greatly in width, especially posteriorly, and also in respect to length. 

 In skulls of the same general size, the width of the nasals posteriorly varies 

 from 0.10 to 0.15 of an inch, or nearly 33 per cent, of the average width. 

 They also vary greatly in respect to their posterior outlines, being generally 

 more or less emarginate, but vary from squarely truncate to deeply emarginate. 

 As already noted in the general remarks upon the genus Sciurus, the first 

 premolar is generally present, though often so minute as to readily escape 

 detection. I find it more frequently present in New England specimens 

 than in those from Fort Simpson, II. 13. T. In the former, it is to he found 

 in about two specimens out of three; in the latter, in only about one in six! 

 It is also pretty uniformly present in Pennsylvania specimens. 



As shown by the subjoined tables of measurements, northern specimens 

 are considerably larger than southern ones. Specimens from Minnesota, and 

 thence westward to the Black Hills, appear to be larger than those from the 

 Fur Countries, as often happens in other species of North American Mammals. 

 On the other hand, Pennsylvania specimens are larger than those from 

 Massachusetts, New Hampshire, and Maine. Taking the skulls as a basis 

 for comparison, twelve skulls from Upton, Me., have an average length of 

 1.73, while ten skulls from Greensburg, Pa., average 1.80. Ten others 

 from Fort Simpson, II. B. T., average very nearly 1.85, or 0.12 (about one- 

 seventh) more than those from Maine. The length of fully adult specimens 

 from Maine and New Hampshire (measured from the end of the nose to the 

 base of the tail) rarely exceeds 6.75, and very often falls below G.50 ; 

 Massachusetts specimens frequently exceed '(.00, and not often fall below G.75 

 while Pennsylvania specimens are still larger. Specimens from the Fur 

 Countries are still larger, apparently averaging 7.75. 



In respect to other geographical variations, specimens from high northern 

 localities are paler and more fulvous than those from the United States, and 

 are more annulated beneath with black. The brightest or reddest specimens 

 in the collection are from New York, Pennsylvania, and Ohio, in which, also, 

 annulations below are infrequent. New England specimens are scarcely 

 different in color from those from the Middle States; Maine specimens being, 



