Bailey North American Species of Sigmodon. 103 



Key to Species. 



1. Tail thinly haired; skull relatively long and narrow. 

 2. Size large, hind foot averaging 32 or more. 

 3. Upperparts mainly warm brown. 



4. Upperparts uniformly brown, size larger - - Mspidus. 

 4 / '. Upperparts brownest on rump, size smaller - spadicipygus. 

 3'. Upperparts light gray, blackish or yellowish gray. 

 4. Upperparts dark gray; much black and no brown littoralis. 

 4'. Upperparts light buffy or yellowish gray. 

 5. Upperparts pale buffy gray. 



6. Pelage fine and not very hispid - -.' - eremicus. 

 6'. Pelage coarse and very hispid, especially in summer. 

 7. Size large, hind foot averaging 40 major. 



7 / . Size medium, hind foot not over 36. 

 8. Hind foot about 33 - * : "- - berlandieri. 



8'. Hind foot 35-36 - . - "' - - '..'-. arizonw. 



5'. Upperparts dark buffy or yellowish gray. 



6. Upperparts buffy gray; hind foot about 34 mascotensis. 

 6'. Upperparts yellowish gray ; hind foot 41 - tonalensis. 

 2'. Size small, hind foot averaging less than 32. 

 3. Upperparts buffy gray - - . - - : " texianus. 



3'. Upperparts tawny or dull brownish gray. 

 4. Upperparts tawny or dull yellowish. 



5. Audital bullae wide and flattened - - - borucce. 



5'. Audital bullae high and narrow, rounded or elongated. 

 6. Tail short, averaging 103; audital bullse narrow saturatus. 

 6'. Tail longer, averaging 112; audital bullae short and 

 rounded alleni. 



4'- Upperparts dull brownish gray. 



5. Belly white; feet clear gray .... toltecus. 

 5'. Belly grayish buff; feet yellowish brown - microdon. 



V. Tail well haired; skull short and wide. 

 2. Upper half of outer surface of ear black. 

 3. Size large, hind foot 30-33. 



4. Upperparts grizzled buffy; lowerparts ochraceous ochrogaster. 

 4'- Upperparts grizzled tawny; belly rich ferruginous melanotis. 

 3'. Size small, foot 28; upperparts gray; belly buffy minimus. 



2'. Outer and inner surface of ears whitish or buffy gray. 



3. Ears buffy gray; nose conspicuously ochraceous ochrognathus. 

 3'. Ears light gray or whitish; nose not conspicuously ochraceous. 

 4. Ears silvery gray; belly white ... - leucotis. 

 4'. Ears darker gray; belly buffy. 



5. Upperparts rich tawny gray - alticola. 



5'. Upperparts dull tawny gray - - - amoks. 



