MAMMALS 325 



C. castanops Baird. Color yellowish brown; buff beneath; length 

 295 mm. ; tail 77 mm. ; hind foot 7,t, mm. : Great Plains from the Arkansas 

 River into Mexico. 



3. Thomomys Wied. Outer surface of upper incisors not grooved 

 or with one fine groove near the median margin (Fig. 1 74) ; ears distinct 

 but very small; claws moderate: many species, all in the Rocky Moun- 

 tain or Pacific States or along the Mexican border. 



Key to the Species of Thomomys 



ai Mammae in 4 pairs. 



bi Size large; length 300 mm. or more. 



Ci Color brown above and below T. bulbivorus. 



C2 Color gray above, buff below T. townsetidi. 



1)2 Size moderate; length under 260 mm. 



Ci Color more or less yellowish (ochraceous). 



di In central and northern California and Oregon T. botfce. 



do In the southern Sierras T. alpimis. 



ds In Arizona, New Mexico and Texas T. fulvus. 



Co Color gray or buff T. perpallidus. 



C3 Color brown. 



di Length over 200 mm. 



ei In northwestern Washington T. douglasi. 



e2 In California and Oregon T. monticola. 



63 In Montana and Idaho T. fuscus. 



do Length 175 mm T. hesperus. 



ao Mammae in 5 or more pairs, 

 bi Mammae in 6 pairs. 



Ci Length over 200 mm T. talpoides. 



Co Length 175 mm T. pygm(Biis. 



bo Mammae in 7 pairs T. ocius. 



ba Mammae in 5 pairs. 



Ci In Colorado and Utah T. fossor. 



C2 In California, Oregon and Nevada T. quadratus. 



T. hott(B (Eydoux & Gervais). Color yellowish brown, darker 

 towards the head; lips and lining of the pockets white; length 260 mm; 

 tail 89 mm.; hind foot 33 mm.; mammae 4 pairs: California. 



Subspecies of T. boUce 



T. b. hottcB (E. & G.). Coast region from Freestone to San Diego. 



T. b. laticeps Baird. Color warmer and brighter: coast region 

 north of Eel River. 



T. b. minor Bailey. Size smaller; color darker: coast region from 

 Cape Mendocino to Cazadero. 



T. b. leucodon Merriam. Smaller, lighter: from Fairfield and 

 Placerville to Grants Pass, Oregon. 



