1915.1 



THOMOMYS UMBRINUS GROUP. 



91 



Distribution. — Known only from type locality (fig. 9); 



Characters. — Considerably larger than umbrinus or peregrinus; 

 hind foot 27-31 nun.; skull heavier; colors dichromatic, usually 

 black, rarely bright umber; ears small; claws slender; mammae in 

 3 pairs. 



Color. — In 14 of 16 topotypes: Glossy iridescent black all over 

 except white on tip of tail, toes, and usually chin and inside of 

 pockets. Two topotypes in brown phase: Upperparts bright burnt 

 umber in the adult, darker in the immature specimen; underparts 

 washed with paler shade of the same or ochraceous-buff ; tip of 

 tail, toes, and inside of pockets white. 



Slcull. — Relatively more elongated, angular, and ridged than in 

 umbrinus or peregrinus; base of zygoma deeply concave, or emargi- 

 nate; lachrymal long and borne mainly on zygoma; premaxillse 

 widening posteriorly and terminating approximately even with 

 nasals; palate flat between molars, but with deep lateral pits and 

 constricted base of pterygoids. Dentition heavy; incisors less pro- 

 jecting than in peregrinus, and plain orange, rarely with white tips; 

 anterior enamel plate of front lower incisor small. 



Measurements. — ^Average of 4 topotypes ( ad.): Total length, 

 219; tail vertebrse, 69; hhid foot, 29.3. Average of 5 females: 132, 66, 

 29. Slcull (of type, 9 ad.): Basal length, 35; nasals, 13; zygomatic 

 breadth, 25; mastoid breadth, 19; alveolar length of upper molar 

 series, 7.7. One topotype ( c? ad.):i 38.5, 14, 25, 19.5, 8. 



Specimens examined. — Sixteen, from type locality. 



THOMOMYS UMBRINUS PEREGRINUS Merriam. 

 Mexican Pocket Gopher. 



(PI. VI, fig. 14.) 



Thomomys peregrinus Merriam, Proc. Biol. Soc. Washington, VIII, 146, Dec. 29, 1893. 



Type. — Collected at Salazar, Federal District of Mexico, Mexico, at 

 10,300 feet altitude, by E. W. Nelson and E. A. Goldman, October 24, 

 1892. Type specimen in U. S. Nat. Mus., Biological Survey collection. 



Distribution. — ^Mountain slopes in the Federal District of Mexico, 

 east to San Martin, Puebla, and north to El Chico, Hildago (fig. 9). 



Characters. — Size medium, sUghtly larger than umbrinus; hind foot 

 27-29 mm.; color dark rich umber; skull with projecting incisors 

 and concave base of zygoma; mammae in 3 pairs. 



Color. — Upperparts dark rich burnt umber, becoming blackish 

 along the back in many specimens; underparts washed with ochra- 

 ceous-buff; feet, tip of tail, and sometimes chin, whitish. A fully 

 melanistic specimen from Santa Rosa, Guanajuato, suggests partial 

 dichromatism. 



iNo. 53611, U. S. Nat. Mus. 



