RODENTIA SCIURINAE SCIURUS. 425 



to be nominal ones, as is not at all unlikely, the number will be reduced to ten from the 

 twenty-four given by Audubon and Bachman. 



There are two strongly marked groups of North American squirrels, each, perhaps, capable 

 of subdivision ; the one, embracing species largest in size, with a long, bushy and full tail as 

 long, with the hairs, at least, as the head and body. The squirrels of the other group are much 

 smaller, the head broader, the muzzle shorter ; the tail, including the hairs, shorter than the 

 head and body, narrow, and flattened ; theae form the transition to the ground squirrels and 

 spermophiles. 



The larger squirrels, again, are divisible into those with four permanent upper molars and 

 those with five. As far as my observations have extended, the former embrace the fox squirrels, 

 or those some varieties of which have the under parts uniform rusty red. The gray squirrels, 

 with their black varieties, belong to the division with five upper molars. All the large western 

 gray squirrels, with white bellies, as Sciurus fossor, aberti, and castanonotus, have five. I am 

 not prepared to say that no fox-colored squirrel has five upper molars, nor that no permanently 

 gray squirrel has four only ; but such is the result of the examinations I have been able to make 

 thus far. 



The following synopsis is intended to exhibit the principal characters of the different groups 

 and species of squirrels : 



GROUP A. Squirrels of large size ; tail very broad, and, with the hairs, longer than the body ; 

 soles mostly naked from the heel in summer. 



Section I. Upper molars permanently four. Kunning into ferruginous varieties, in which the 

 bones are red. 



Species 1. Ears and nose always white S. vulpinus. 



Species 2. Ears never white ; head broad ; ears short, scarcely longer than 



the adjacent fur S. cinereus. 



Species 3. Ears never white ; head narrower ; ears high S. ludovicianus. 



Species 4. Similar to the last, but much smaller; prevailing colors cinna 

 mon S. limitis . 



Section 2. Upper molars permanently five. Ferruginous varieties rare. Colors generally 

 gray above and white beneath. Dusky or black varieties in one species. 



Species 5. Without a black lateral line ; tail, even with the hairs, but little 

 longer than the body. Above grizzled light yellow, with oc 

 casional washes of yellowish rusly gray. (Some black varie 

 ties.) S. carolinensis. 



Species 6. Without a black line ; vertebrae of tail alone, nearly, or quite as 

 long as the body. Above uniform grizzled dark, plumbeous 



gray , S. fossor. 



Species 7. With a black lateral line ; a chestnut dorsal stripe; ears tufted. ..& aberti. 



Species 8. Similar to the last; ears not tufted S. castanonotus. 



GROUP B. Squirrels of small size ; tail narrow, even including the hairs, shorter than the 

 body ; muzzle short ; hind feet, in summer, naked beneath for one-half or one-third their length 

 from the heel ; anterior small upper molar either wanting or, when persistent, very small and 

 thread-like ; a black stripe on the flanks ; back of the ears more or less tufted in winter. 



