1914.] KEITHKODON"TOMYS CHEYSOPSIS GROUP. 67 



Distrihution. — High mountains around the valley of Mexico; Mount 

 Patamban and Mount Tancitaro in Michoacan. Altitudinal range 

 from 9,000 feet to 13,500 feet (timber line). 



Characters. — Size large (almost equaling R. Jiirsutus); tail long; 

 pelage very long, soft, and silky; ears black or blackish; tail bicolor; 

 skuil with rounded and much inflated braincase; bullae large. 



Color. — ^Upperparts a rich shade of ochraceous, between ochraceous- 

 buff and orange-buff, rather heavily mixed on back with blacky the 

 latter color usually forming an indistinct median band; general tone 

 of sides near pinkish cinnamon; ears fuscous-black; tail sharply 

 bicolor, fuscou.s above, grayish white beneath; feet grayish white; 

 ankles fuscous; underparts strongly suffused with light pinkish cin- 

 namon. 



SlcuU. — Of large size (considerably exceeding that of R. r. rufescens); 

 braincase subglobular, usually much inflated, sometimes moderately 



Fig. 5. — Distribution of Reithrodontomys chrysopsis, E. perotensis, R. levipes, R. Mrsutus, and subspecies. 



flattened; zygomata slender, strongly contracted anteriorly; outer 

 j waU of anteorbital foramen broad; rostrum slender, narrowing 

 j gradually to the tip ; audital bullae very large and moderately inflated ; 

 interpterygoid fossa relatively narrow (compared with R. levipes); 

 palatal foramina long (as in rufescens); upper molars with sub- 

 sidiary enamel loops in primary angles, but these usually not reaching 

 outer border of tooth; accessory tubercles absent or much reduced. 



Measurements. — Type: Total length, 194; tail vertebrae, 108; hind 

 foot, 21. Average of 5 specimens from Ajusco, Salazar, and Huit- 

 zilac: Total length, 185 (177-188); tail vertebrae, 106 (98-111); 

 hind foot, 20.8 (20-21). Skull: (See table, p. 81). 



Reraar'ks. — This handsome and striking species is an inhabitant of 

 I the upper slopes of the mountains about the valley of Mexico and on 

 more or less isolated mountains in western Michoacan. It is the 

 first-described and best-known member of a subalpine group of 

 r species found on most of the higher mountains of southern Mexico 



