1915.] 



THOMOMYS UMBRINITS GROtJP. 



89 



Color. — ^Upperparts dull ochraceoiis-tawny or grayish buff; nose 

 and ear patch dusky; underparts pale cinnamon to soiled whitish; 

 feet whitish. 



STcull. — Eesembling that of aureus m general form, with full rounded 

 bullae, narrow basioccipital, and slightly arched palate, but differ- 

 ing in its smaller size, slenderer form, and less-ridged surface; inter- 

 parietal normally quadrate; slender points of premaxillse extending 

 far back of truncate or slightly emarginate tip of nasals. 



Measurements. — Type ( ad.): Total length, 215; tail vertebrae, 

 65; hind foot, 29. Average of five topotypes ( ad.): 202, 61, 27. 

 Average of three females: 195, 62, 26. SliuU (of type) : Basal length, 

 35; nasals, 14; zygomatic breadth, 22; mastoid breadth, 19; alveolar 

 length of upper molar series, 7. 



Remarlcs. — This form needs no comparison with haileyi on the 

 east or perditus on the south. It was originally, but probably erro- 

 neously, considered a small, dull-colored desert form of aureus. It 

 occupies the arid Lower Sonoran mesas, but apparently does not occur 

 in moist and fertile bottom lands as do the more robust aureus and 

 toltecus. Specimens from Presidio County and the Great Bend region 

 are not typical, but they vary so much with each locality that 

 to avoid making more subspecies I have referred them to this, the 

 nearest form. It seems probable that the great variation in the 

 gophers of this region is due to the scarcity of individuals and the 

 isolation of colonies. 



Specimens examined. — -Total number, 33, as follows: 

 Chiliuah.ua: Casas Grandes, 2. 



New Mexico: Organ, 2; Organ Mountains, 2. - 



Texas: Alpine, 1; Boquillas, 2; El Paso, 12; Franklin Mountain (10 miles north 



of El Paso, 4; and 15 miles north, 2), 6; Marathon (15 miles south), 1; Paisano, 



1; Presidio County (35 miles south of Marfa), 4. 



Thomomys umbrinus Group. 



THOMOMYS UMBRINUS UMBRINUS (Richardson). 

 Southern Pocket Gopher. 



(PI. II, fig. 13; PI. VI, fig. 13; text fig. 2.) 



Geomys umbrinus Richardson, Fauna Boreali-Americana, I, 202, 1829. 

 Thomomys umbrinus Bailey, Proc. Biol. Soc. Washington, XIX, 3, Jan. 29, 1906. 



Type —In British Museum, said to have come from Cadadaguios, 

 a town in southwestern Louisiana," but no such town has ever been 

 located, except the Kadhoadacho Indian settlements on the Ked 

 River, in western Louisiana, where Thomomys does not occur. The 

 type locality is now restricted to Boca del Monte, Vera Cruz. Type 

 identified with specimens from Vera Cruz.^ 



1 Proc. Biol. Soc. Washington, XIX, 3, Jan. 29, 1906. 



