222 THOMOMYS. 



Upper incisors without median sulcus, but with a fine marginal 

 groove, not, however, always present. Roots of inferior incisors 

 forming a protuberance on outside of condylar ramus; zygomata 

 wider posteriorly than mastoid diameter of skull. Audital bullae 

 inflated; basioccipital narrower in the middle than bulls at same 

 place. Pterygoid fossa rather short, and wide posteriorly. Upper 

 molars with e-xterior edge of crown acute; lower molars with interior 

 edge acute. Fore claws moderately developed. 



Lower tooth kow. 

 Enlarged 4 times. 



Fig. 52. Thomomys bottae. 

 Field Columbian Museum Coll. Nat. size. 



Upper tooth row. 

 Enlarged 4 times. 



329. bulbivorus. {Diplostomd), Richards, Faun. Bor. Amer., 1829, i, 

 p. 206, pi. 18, B. 



Type locality. Columbia River. 



Geogr. Disir. Lower Columbia River, Oregon, to coast of Cali- 

 fornia north of San Francisco. 



Genl. Char. Size very large; tail short, little more than one-third 

 head and body; claws large, strong; color dark; pterygoids concave 

 internally, hamulars converging at the tips. 



Color. Above ^'elIowish chestnut, darkest on top of head; lips. 



