1915. ] 



THOMOMYS UMBKINUS GKOUP. 



95 



like peregrinus, through which goldmani evidently connects with the 

 umhrinus group. 



Specimens examined. — Total number, 9, as follows: 

 Durango: Diirango, 6; Mapimi, 2; San Gabriel, 1. 



THOMOMYS PERDITUS Merriam. 

 Little Gray Pocket Gopher. 



(PI. VI, fig. 9. ) 



Thomoviys perdifus Merriam, Proc. Biol. Soc. Washington, XIV, 108, July 19, 1901. 



r^/pg.— Collected at Lampazos, Nuevo Leon, Mexico, by Clark P. 

 Streator, January 22, 1891. Type specimen in U. S. Nat. Mus., 

 Biological Surrey collection. 



Distribution. — Eastern Coahuila and western Nuevo Leon, north 

 to Kock Springs and Castle Mountains, western Texas (fig. 9). 



(Jharacters. — Size small, hind foot 25 mm.; color huffy gray or pale 

 tawny; skull short and narrow, with slightly projecting incisors; 

 mammae in 3 pairs, inguinal 2-2, pectoral 1-1. 



Color. — Upperparts dark huffy gray or pale dull tawny, darkest 

 along back; sides brighter; belly and feet pale huffy or creamy white; 

 ear patch, nose, and lips dusky; inside of pouches white. 



SlcuU. — Short, with smooth, rounded braincase and rectangular 

 zygomatic arches; incisors projecting slightly beyond nasals; nasals 

 sharply notched posteriorly and terminating on a plane with short 

 premaxiUss; interparietal normally quadrate, wider than long; ante- 

 rior base of zygoma strongly convex in outline, unhke most species of 

 the umhrinus group. 



Measurements. — Type ( ad.): Total length, 195; tail vertebrae, 

 59; hind foot, 26.5. Average of 2 topotypes ( ad.): 192, 58, 26.8. 

 Average of 2 females: 180, 54, 24.5. SlcuU (of type): Basal length, 

 33; nasals, 12; zygomatic breadth, 21; mastoid breadth, 18; alveo- 

 lar length of upper molar series, 7. 



RemarTcs. — The relationships of this species, as exhibited by the 

 cranial characters, seem not to be very close with any of the surroimd- 

 ing forms, but the number and arrangement of mammae place it in 

 the umhrinus group. 



Specimens examined. — Total number, 24, as follows : 



Coahuila: Carneros, 5; Jaral, 1; Sierra Encarnacion, 1; Sierra Guadalupe, 4. 

 Nuevo Leon: Lampazos, 5; Villadama, 2. 



Texas: Castle Mountains, 1; Comstock, 2; Devils River, 1; Rock Springs (35 

 miles east), 1; Samuels, 1. 



THOMOMYS ATROVARIUS Allen. 

 Black-and-Brown Pocket Gopher. 



(PI. VI, fig. 16.) 



Thomomys atrovarius Allen, Bui. Am. Mus. Nat. Hist., X, 148, 1898. 



Type. — Collected at Tatemales (near Rosario), Sinaloa, Mexico, by 

 P. O. Simons, May 15, 1897, Type specimen in the British Museum. 



