92 



NORTH AMEBICAN FAUNA. 



[no. 39. 



SlcuU. — Less markedly short and wide than in umhrinu8 and with 

 sHghtly less projecting incisors; base of zygoma slightly concave; palate 

 flat between molar series, and unique in having shallow lateral pits 

 and wide base of pterygoids. Dentition light; incisors bright orange 

 with white tips ; anterior enamel plate on front lower incisors small but 

 distinct and constant. 



Measurements. — Average of 3 topotypes ( <2' ad.) : Total length, 

 208; tail vertebrae, 61; hind foot, 28. Average of 5 females: 189, 

 59, 27.3. STcuTl (of type, $ ad.): Basal length, 34; nasals, 12; zygo- 

 matic breadth, 23 ; mastoid breadth, 18; alveolar length of upper molar 

 series, 7. SkuU of topotype ( j ad.):^ 34, 12.3, 24, 19, 7. 

 Specimens examined. — Total number, 43, as follows: 

 Hidalgo: El Chico (Sierra de Pachuca), 3; Real del Monte, 3; Tulancingo, 1. 

 Mexico: Popocatepetl, 1; Salazar, 17; Toluca Valley, 1; Volcan Toluca (north 



slope), 15. 

 Puebla: San Martin, 2. 



THOMOMYS NELSONI Merriam. 



Nelson Pocket Gopher. 

 (PI. VI, fig. n.) 



Thomomys nelsoni Merriam, Proc. Biol. Soc. Washington, XIV, 109, July 19, 1901. 



Type. — Collected at Parral, Chihuahua, Mexico, at 6,000 feet alti- 

 tude, by E. W. Nelson and E. A. Goldman, September 18, 1898« Type 

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



Distribution. — Central Chihuahua, from Gallego south to Parral 

 (fig. 9). 



Characters. — Size small, hind foot 28 mm.; color bright tawny; 

 skull short and wide, with projecting incisors. 



Color. — Winter pelage: Upperparts light russet or bright tawny, 

 darker along back and on face; nose and ear patch blackish; ankle 

 and base of tail brownish, lower part of feet and terminal part of tail 

 white; belly pale tawny. Summer pelage: A shade brighter above 

 and below. 



SJcull. — Short and wide with abruptly spreading zygomata and 

 strongly projecting, lightly grooved, white- tipped incisors; nasals 

 narrow, cuneate, slightly notched, and terminating a little short of 

 the wide posterior tips of premaxillse; basioccipital wide and flat; 

 frontals wide, crowding slightly into base of zygomata; lachrymal 

 mainly adnate to zygoma. 



Measurements. — Type ( j ad.):^ Total length, 196; tail vertebrae, 

 60; hind foot, 28. Topotype ( c? ad.) : 207, 59, 28.5. Shull (of type) : 

 Basal length, 37; nasals, 13; zygomatic breadth, 24; mastoid breadth, 



iNo. 50122, U. S. Nat. Mus. 



2 The type of nelsoni was marked " on the original label and referred to in original description as 

 female. It is, however, a fine old male with prominent sex marks showing in the skin and with the skull 

 characters of the male. 



