MONOGRAPH OF THE GENUS SCIURUS. 389 



of the anterior portions on the ears; the nose is white, which 

 colour extends along the forehead till above the eyes, where 

 it is gradually blended with the colours on the back. The 

 cheeks are white, a little greyish beneath the eyes. The whole 

 of the under surface, including the feet and inner surface of 

 the legs, pure white to the roots. In the tail the colours are 

 irregularly blended, with markings of black, brownish yellow 

 and white. In general it may be said that the tail, when ex- 

 amined without reference to rudimental hairs, is light ash at 

 the roots of the hairs, then a broad but not well defined line 

 of light rufous, then dark brown, and tipt with rufous and 

 smoke grey. 



DIMENSIONS. 



IN. L. 



Length of head and body 7 11 



Tail (yertebrce) 4 8 



Ditto including fur 6 



Palm and middle fore claw 1 



Sole and middle hind claw 1 9 



Length of fur on the back „ 7 



Length at the tip of the tail 1 10 



Height of ear posteriorly, including fur „ 5 



On the back and in the tail there are so many white hairs 

 interspersed, and the white spot on the head being merely oc- 

 casioned by a greater number of hairs nearly or wholly white, 

 that there is great reason to believe that this species becomes 

 much lighter, if not wholly white, during winter. 



In the shape of the head and ears, and in the pointed pro- 

 jections of the teeth, this species approaches the marmots and 

 spermophiles ; but in the shape of its body, — its soft fur, — its 

 curved and acute nails, constructed more for climbing than 

 digging in the earth, — and in the third toe being longer than 

 the second, — it must be placed among the squirrels. 



In attempting a Monograph of the genus Sciurus, I have 

 confined myself to descriptions of those species only, which 

 are either found in the United States of America, and in the 

 northern parts of that continent, or such as have been disco- 

 vered along the range of the Rocky Mountains, as far west as 

 the Pacific Ocean, extending to California. The squirrels of 

 Mexico, of which there are several species, including Sciurus 

 hypopyrrhus (Wagler), Sci. albipes and Set. socialis (Wagner, 

 Beitrage zur Kenntniss der warmblutigen wirbelthiere Ame- 



