THOMOMYS. 333 



Upper incisors without median sulcus, but with a fine marginal 

 groove, not, however, always present; root of inferior incisors form- 

 ing a protuberance on outside of condylar ramus; zygomata wider 

 posteriorly than mastoid diameter of skull ; audital bullae inflated ; 

 basioccipital narrower in the middle than bullae at same place, 

 pterygoid fossa rather short, and wide posteriorly; upper molars 

 with exterior edge of crown acute; lower molars with interior edge 

 acute; fore claws moderately developed. 



FIG. 64. THOMOMYS ATROVARIUS. 



No. 13769 Am. Mus. Nat. Hist. Coll. Nat. size. 



KEY TO THE SPECIES AND SUBSPECIES. 

 A. Upper incisors without median grooves; fore 

 claws weak. 



a. Upper parts yellowish brown or fulvous. 



a/ Under parts yellowish white, tinged with PAGE 



rufous T. fulvus 334 



b.' Under parts buff T. /. anitce 335 



c.' Under parts reddish fulvous T. f. alticola 335 



b. Upper parts tawny brown, beneath tawny 



ash T. f. nigricans 335 



c. Upper parts dark mars brown T.f. intcrmedius 336 



d. Upper parts grayish brown and blackish, 



beneath grayish white T. martirensis 336 



