57. With conspicuous tufts of long hairs on the ears; Colo, southwards 58. 

 No conspicuous ear tufts 59. 



58. White beneath; Colo, southwards 



Scnirus aherti Woodhouse Tuft-eared Squirrel 

 Black beneath; Arizona 



Sciurus \aihahensis Merriam Kaibab Squirrel 



59. Small; adults seldom reaching fourteen inches in total length; rustyred 



above and white to rusty below; first upper premolar vestigial to 



absent 60. 



Larger; adults reaching seventeen to twenty inches in total length; first 



upper premolar usually present; chiefly grayish above 62. 



60. Under parts rusty-red; west of the Rockies 



Tarmasciurus douglasii (Bachman) Western Chickaree 

 Under parts whitish or dusky 61. 



61. Hairs of tail tipped with white; in southern Rocky Mountain states 



Tamiasciurus fremonti (Audubon 5? Bachman) 

 Fremont Chickaree 

 Hairs of tail with yellowish tips; in northern Rocky Mountain states and 

 most of the forested area east of the Rockies 



Tamiasciurus hudsonicus (Erxleben) Red Squirrel, Chickaree 



62. Color of back a brownish-gray mixture, with gray predominating; in 



forested areas of the eastern and central states; introduced in some 

 western states 



Sciurus carolinensis Gmelin Eastern Gray Squirrel 

 Color of back silvery-gray; tail very broad, with the hairs often three 

 inches long; Pacific states 



Sciurus griseus Ord Western Gray Squirrel 



63. Thick-bodied mammals with very short legs; fore feet much enlarged for 



digging; eyes and ears very small; Family Geomyidae Pocket Gophers 



64. 



Small, slender mammals, usually adapted for leaping; eyes and ears usual' 



ly large; tail about as long as the body, often with a terminal tuft of 



hair; Family Heteromyidae Pocket Mice and Pocket Rats 80. 



64. Outer surface of upper incisors not grooved or with a shallow groove near 



the inner edge; lower molars with anterior as well as posterior plates 

 of enamel; Rocky Mountain and Pacific states Western Pocket 

 Gophers 65. 



Outer surface of upper incisors each with an almost central groove or 

 with two grooves, the deeper one near the outer edge; lower molars 

 with enamel plates posteriorly only 76. 



65. Upper incisors protruding beyond tip of nasal bones 66. 

 Not so 69. 



66. Ears small but pointed; Idaho and Nevada 



Thomomys townsendii (Bachman) Townsend's Pocket Gopher 

 Ears merely a thickened rim 67. 



67. Incisors projecting slightly; Cal., Ariz,, and Utah 



Thomomys hottae (E. ^ G.) California Pocket Gopher 

 Incisors projecting markedly 68. 



510 



