1915.] 



THOMOMYS PEEPALLIDUS GROUP. 



71 



THOMOMYS PEEPALLIDUS CHRYSOXOTUS GRmNELL. 

 Yellow-Backed Pocket Gopher. 



Thowomys chrysonotiLS Grinnell. Univ. of Cal., Piibl. ZooL. X. 174, 1912. 



Tyjpe. — Collected at Etirenburg, Aiizona, (on dry mesa back from 

 river bottoms), by F. Stephens, March 27, 1910. Type specimen in 

 Mus. Vert. ZooL, Univ. of California. 



Distrihution. — Southwestern Arizona and northwestern Sonora, 

 from Ehrenberg south to near mouth of Colorado River, and east to 

 Quitobaquiio (figs. 7 and 8). 



Characters. — Size smaller than perpaUidus; ears minute; skull 

 shorter, and bullae more globose; color about the same; mammae in 

 4 pairs. 



Color. — Summer pelage: Upperparts bright to pale buff; ears brovvm 

 or dusky at tips; postauricular patch generally inconspicuous; 

 nose brownish; underparts and well up on sides whitish with pale 

 plumbeous base of hair; feet and tail thinly clothed with short white 

 hairs. Winter pelage: More grayish, fading to very pale buff in early 

 spring. 



Shull. — Short and wide; rostrum relatively shorter and wider than 

 in perpallidus: bullae fuller and more rounded; upper incisors more 

 abruptly decurved: premaxillse in type ending approximately even 

 with posterior tip of nasals, but in the majority of specimens extend- 

 ing well back of nasals; interparietal small and nearly triangular; 

 pterygoids short, thick, low, and wide apart.- 



Measurements. — Type ( ad.); Total length, 217; tail vertebra, 

 73; hind foot, 30. Adult female from Yuma, Ariz.; 203, 65, 27. 

 Slcull (of type) : Basal length, 33.5; nasals, 13.5; zygomatic breadth, 

 23; mastoid breadth, 19; interorbital breadth, 7; alveolar length of 

 upper molar series, 8. 



Remarks. — This seems to be a dry-mesa form more nearly agreeing 

 with typical perpallidus than with the more robust alhatus of the 

 moist bottoms just across the Colorado River. Originally I identified 

 the type for Dr. Grinnell as perpallidus, but since that time he has 

 collected a fine series of topotypes of perpallidus at Palm Springs, 

 which show better diagnostic characters than do the series in the 

 National Museum collection, and fully warrant the separation of 

 the form ranging in the dry hot desert east of the Colorado River 

 in southwestern Arizona and northwestern Sonora. 



Specimens examined. — -Total number, 25, as follows; 

 Arizona: Ehrenburg, 1; Monument Xo. 204, east side of Colorado River, 1; 

 Quitobaquito, 2; Tacna. 1: Tule AVells (in Tule Mountains near Sonora line), 

 •5; Yuma, 12. 



Sonora: Cienega Well. 2; Mesa on east side of Colorado River, 20 miles below the 

 Aiizona line, 1. 



