248 BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



Genus SCIURUS Linn^us (17S8). 

 Sciurus Linnyeus, Syst. Nat, lOtb ed.. 1758, p. 64. 



Tail long and bushy ; ears well developed, sometimes tufted. Feet 

 adapted for climbing, the anterior having 4 digits and a rudimentary 

 pollex and the posterior 5 digits, all of which have long, curved, 

 and sharp claws. Skull lightly built, with long postorbital processes ; 

 penultimate upper premolar, when present, minute. Mammae in the 

 species on the Mexican border, 4 pairs. Diurnal and arboreal. 



KEY TO SCIURUS FOUND ON THE MEXICAN BOUNDAUY LINE, BA.SED ON EXTERNAL CHARACTERS. 



a. Total length about 400 mm. 

 6. Pelage mostly rufescent above. 



c. Median area of upper and under side of tail narrow and obscure, with 

 the color of this part reddish above and gray below. 



Sciurus fremonti mogollonensis (p. 256). 

 cc. Median area of upper and under side of tail broad and distinct, yellow- 

 ish ochraceous above and grayish white below ; general color of body 

 slightly yellower and less rufescent above. 



Sciurus fremonti grahamensis (p. 261). 



J)b. Pelage mostly grayish above Sciurus mcarnsi (p. 262). 



aa. Total length more than 400 mm. 



d. Ears conspicuously tufted ; sides with a line of black separating the 

 colors of the upper and lower surfaces ; under surface of tail white. 



Sciurus aberti (p. 250). 

 dd. Ears not tufted ; sides without a black line : under side of tail white. 

 e. Under surface of body ochraceous. 



/'. Upper surface with a black vertebral band; length, 554 mm.; tail, 



279; hind foot, 77 Sciurus apache (p. 270). 



ff. Upper surface without a vertebral band ; length, 475 mm. ; tail, 



225; hind foot, 66 Sciurus ruflventer texianus (p. 281). 



ee. Under surface of body white. 

 g. Hair of tail fulvous at base. 



7(. Back and ears uniform gray ; total length less than 500 mm. 



Sciurus alleni (p. 269). 

 /(/(. Back and ears rusty yellowish : length more than 500 mm. 

 i. Rusty band continuous fi-om occiput to root of tail. 



Sciurus arizonensis (p. 273). 

 ii. Rusty dorsal band interrupted anteriorly. 



Sciurus arizonensis huachuca (p. 277). 



gg. Hair of tail gray at base; total length, 575; tail, 290; hind 



foot, 80 Sciurus griscus antlionyi (p. 264). 



KEY TO SCIURUS FOUND ftN THE MEXICAN BOUNDARY LINE, BASED CHIEFLY ON CRANIAL AND 



DENTAL CHARACTERS. 



a. Species having two upper premolars. 

 6. Total length of skull less than 60 mm. 

 c. Pelage mostly rufescent above. 



d. Median area of upper and under side of tail narrow and obscure, 

 with the color reddish above and gray below. 



Sciurus fremonti mogollonensis (p. 256). 



