SQUIRRELS OF MEXICO AND CENTRAL AMERICA 57 



Distribution. — Oak and pine forests of Transition and Boreal zones 

 on Mts. Popocatepetl and Iztaccihuatl, in States of Mexico, Puebla, 

 and Morelos (alt. 8000 to 12,000 ft.). 



Characters. — Similar to S. nelsoni but differs in having a dark 

 iron gray area on middle of back, grizzled gray feet, and dingy fur- 

 ruginous underparts. Pelage thick and soft ; under fur long; tail ex- 

 tremely broad and bushy. Teats : p.i a. -| i. \. 



Color. — Crown, nape, and rump dingy grizzled yellowish or gray- 

 ish brown; top of nose, middle of back (often reaching down on out- 

 side of legs) finely grizzled bluish gray; feet gray, toes paler; ears 

 similar to crown, with conspicuous white basal patches ; chin and 

 lower cheeks dull gray ; underparts dingy ferruginous ; tail above, 

 black heavily washed with-white ; below, median area grizzled yellow- 

 ish or rusty brown, with black border and thin white edge. Hairs on 

 gray area of back black, with short white tips, scantily mixed with 

 similar hairs having narrow median or subterminal rings of dull buffy. 



Variation. — The gray area is sometimes an enclosed spot on mid- 

 dle of back and sometimes covers most of the upper surface; the gen- 

 eral color is lighter and less sooty than in nelsofii, and the wash on 

 tail is white. The ferruginous of underparts varies from light rusty 

 to dark dull rufous. One specimen from Tochimilco has black ears 

 and feet and a small patch of gray on middle of back, but can be recog- 

 nized at once by the other characters. Two winter specimens from 

 Mt. Popocatepetl can be distinguished from summer specimens from 

 Tochimilco by the general grayness of the upperparts. 



Meas2ire?nents. — Average of five adults from type locality : total 

 length 514.2 ; tail vertebriE 256.8; hind foot 68. 



Cranial characters. — Premolars |. Skull like that of S. aureolas- 

 ter. Five adult skulls from type locality average : basal length 50.2 ; 

 palatal length 26.5; interorbital breadth 19.4; zygomatic breadth 35.1 ; 

 length of upper molar series 11.8. 



General notes. — This subspecies seems to be peculiar to the Vol- 

 cano of Popocatepetl, and probably Iztaccihuatl immediately adjacent. 

 One specimen came from near timberline on the north slope of Popo- 

 catepetl, the others from Tochimilco on the southeast slope, and Tetela 

 del Volcan on the south slope. 



Specimens examined. — Seven : from Tochimilco, Puebla ; Mt. Po- 

 pocatepetl, Mexico; and Tetela del Volcan, Morelos. 



