THOMOMYS. 33833: 
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 bulle inflated; 
basioccipital narrower in the middle than bulla 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 
Fic. 64. THOMOMYS ATROVARIUS. 
No. 13769 Am. Mus. Nat. Hist. Ce Nat. size 
BEY TO TRE 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 PAGI 
rufous T.fulvus 334 
b.’ Under parts buff Lj. Qnne ~ 335 
ec.’ Under parts reddish fulvous Tf. fj. aliscola. 3355 
b. Upper parts tawny brown, beneath tawny 
ash ; T. 7. nigricans 335 
c. Upper parts dark mars brown T.j.antermedius 336 
d. Upper parts grayish brown and _ blackish, 
beneath grayish white mio pe: T.martirensis 336 
