1915.] 



TH0M0MY3 UMBEIXUS GROUP. 



93 



21; alveolar length of upper molar series, 7. Skull of male topotype: 

 34, 12, 24, 19.5, 7. 



Remar'ks —The short, wide skuU, projecting incisors, and white shp- 

 pers and tip of tail reveal relationship with the umhrinus group, 

 although in the specimens collected there are no females to show the 

 arrangement of mammse. However, nelsoni is evidently a northern 

 form of the group. 



Specimens examined. — Total number, 3, as follows: 

 Chihuahua: Gallego, 1; Pan-al, 2. 



THOMOMYS SHELDONI.i sp. nov. 

 Sheldon Pocket Gopher. 



(PI. VI, fig. 12.) 



Type from Santa Teresa (6,800 feet altitude), Tepic, Mexico. 

 Adult d , No. 90819, U. S. Nat. Mus., Biological Survey collection. 

 Collected August 10, 1897, by E. W. Nelson and E. A. Goldman; col- 

 lectors' number, 11443. 



Distrihution . — Transition Zone on the Sierra Madre, Mexico, from 

 northern Chihuahua south to Guanajuato (fig. 9). 



CTmracters. — In size slightly larger than umhrinus or peregrinus, 

 and more brightly colored than either; ears small; claws slender; 

 skull relatively long, with long nasals and not very protruding incisors ; 

 mammae in 3 pairs. 



Color. — Summer pelage: Upperparts light umber, or russet-brown, 

 darker along median line of back, on nose, and about ears; under- 

 parts lighter, more tawny; lower half of feet and tip of tail usually 

 white; rarely any white on chin or throat in typical series; white 

 lining of cheek pouches scarcely showing. Young duller and darker. 



Slcull. — Relatively longer than in other members of the group, 

 with longer, narrower nasals and slender rostrum ; interorbital region 

 wide and flat; interparietal triangular; nasals slightly emarginate, 

 usually falling short of posterior tips of premaxillse; anterior base of 

 zygoma nearly straight, in some slightly concave and in others 

 sUghtly convex; lachrymal adnate to zygoma for over half its length. 

 Dentition: Incisors moderately projecting, dark orange, with small 

 but distinct grooves along inner margins. 



Measurements. — Type ( c? ad.) : Total length, 210; tail vertebrae, 

 64; hind foot, 29. Average of 4 topotypes ( c? ad.): 200, 62, 28.8. 

 Average of 4 adult females:- 191, 61, 28.5. ShuU (of type): Basal 

 length, 37; nasals, 14.5; zygomatic breadth, 25; mastoid breadth, 

 19; interorbital breadth, 7; alveolar length of upper molar series, 8. 



RemarJcs. — This is a northern form of the umhrinus group, occupy- 

 ing the Transition Zone of the main Sierra. Madre of Mexico, and 



iXamed for Charles Sheldon in recognition of his interest in mammals, large and small, and his many 

 contributions of specimens and of notes on their habits. 



