244 U. S. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



maximum size, as S. vvlpinu8 y cinereus, carolinensis, &c. ; and that having S. hudsonius as its 

 type, characterized by smaller size, shorter and thinner tail, and shorter muzzle. This short 

 ness of the muzzle is strikingly shown in the skull, which is very broad and full, much more 

 convex longitudinally and transversely, and with the nasal bones one fourth the length of the 

 skull instead of one third. 



The determination of the species of squirrels of North America has always been a matter of 

 great difficulty, owing to many different reasons. The species themselves exhibit an unusual 

 tendency to run into varieties of color, among which red, gray, and black are the predominating 

 ones, with all possible intermediate shades ; these varieties are sometimes more or less constant 

 in particular localities, sometimes changing with every litter. I am not aware that there is 

 any material difference of color at different seasons or ages in the same animal. 



Another source of perplexity to the naturalist is the alteration in average size with the lati 

 tude. Many of our animals become smaller as we proceed southward, until, on the sea coast of 

 Georgia, Florida, and the Gulf they reach their minimum. This is very strikingly seen in the 

 common deer, which on the sea islands of Georgia is so small as to be readily lifted and thrown 

 across a horse with perfect ease by a man of ordinary strength. 



It is in the Sciuridae that, next to the deer, we find this law to prevail most decidedly. 

 Nearly all the species of extensive north and south range will be found, on careful examination, 

 to substantiate this position. 



A similar variation in color to that of the squirrels is seen in the foxes and wolves, most 

 strikingly in the former. It is now well known that the red, cross, and black foxes are identical 

 in species, the same litter frequently embracing all the colors, and that some of these varie 

 ties again are more or less permanent, while the more boreal the locality the greater tendency 

 to black. This is the case also with the squirrels, where the smaller species assume the black 

 pelage to the greatest extent in the more northern portions of the United States. 



As a general rule it may be stated that where a squirrel exhibits any annulation of the fur on 

 the throat or belly it is a variety of some species, typical specimens of which have the under 

 parts either uniformly white or reddish to the roots, which, however, are sometimes plumbeous. 

 In every such instance that has come under my examination I have had no difficulty in tracing 

 it to its proper type. Such annulation is usually accompanied by a duskier color of the pelage. 

 The tendency to annulation below is strongest in the squirrels of the Mississippi Valley, and 

 applies both to gray and fox-colored species. No such instances of annulation have yet come 

 under my notice among the squirrel*; west of the Eocky Mountains. 



As a general rule the bones of the entire skeleton of the fox squirrels, or those with rusty 

 bellies, are red, while the white bellied varieties have them white. 



After carefully examining a large number of American squirrels I have reluctantly come to 

 the conclusion that very many of the species now borne on our scientific records must be 

 dropped, or reduced to the position of temporary or local varieties. I hope to be relieved from 

 the imputation of wanton and unnecessary reduction in the number of species when I state that 

 the species already published as new by myself have in nearly every case shared the fate of 

 others older in date. The nominal species have usually been based on the varying size or dif 

 ferent colors of different specimens. The dusky varieties and those with the hairs of the under 

 parts annulated have in nearly every instance been raised to the rank of a distinct species. 



In the following pages it will be seen that I recognize only twelve species of squirrels as 

 satisfactorily proved to belong to the United States, and should S. limitis and castanonotus prove 



