MAMMALS OF THE MEXICAN BOUNDARY. 249 



(Id. Median area of upper and under side of tail i»road and distinct, 

 yellowish oehraeeous above and grayish white below ; general 

 color slightly yellower and less rufescent above. 



SciiirKs frenionti graliaviensis (p. 261). 



CO. Pelage mostly grayish above Sciunisi mcarvsi (p- 202). 



bb. Total length of skull more than 00 mm. 



e. pm^ large; interpterygoid fossa short, about equaling the three upper 

 true molars ; incisive foramina short, nearly as wide as long ; skull 



measuring 01 by o6 mm Srim-iis aherti (p. 2.50). 



ee. pm^ small ; interpterygoid fossa longer, measuring, from base of ptery- 

 goid, more than the three upper true molars. Skull measuring 08 by 



?y9 mm Sciiirus griscus anHiotiyi (p. 204). 



aa. Species with only one upper premolar. 

 f. Size small. 



0. Skull measuring 51 by 34 mm. in greatest dimensions. 



Hritiriis aUeiii (p. 200). 

 {/(/. Skull measuring 01 by 3~t uuu. in greatest diameters. 



Sciurus rufi venter texianiis (p. 281). 

 ff. Larger. 



h. Skull high, measuring 03 by 37 to 6.5 by .38 mm. ; brain case 

 inflated and bulging behind the orbits, where the frontal bone 

 forms the anterior portion of its roof. 

 i. Skull smaller ; rusty yellow band continuous from occiput to 



root of tail tSeinriis arizonensis arizonensis (p. 273). 



a. Skull larger ; rusty yellow dorsal band interruiited ante- 

 riorly Sciiinis arizo)ie)isi.s hiKicJiuca (p. 277). 



hh. Skull low, measuring 0.5 by 37 mm. ; brain case less inflated. 



.S'cJM/-Hs apache (p. 270). 



Subgenus OTOSCIURUS Nelson (1899). 

 TTJFT-EARED PIME SQUIRRELS. 



Otosciiirus Nelson, Proc. Washington Acad. Sci., I, p. 28, May 9, 1899. 



DentUicm.^l. I^J; F. f^; M. |f|=22 



Tyye. — Sciurus aberti Woodhouse. 



Type-locality. — San Francisco Mountain, Arizona. 



Gliaracters. — Compared with other North American arboreal squir- 

 rels, the skull is short and broad ; frontal area flattened ; brain case 

 depressed, inflated laterally (but less so than in typical Schirus) : 

 rostrum and nasals long, the latter equaling interorbital breadth; 

 premolars f; ears long and broad, very heavily tufted in winter; 

 color usually mainly gray above, ^yllite below, with a lateral line more 

 or less distinctly black. 



This subgenus is very closely related to typical Sciurus, of which 

 Sciurus vulgaris Linnaeus is the type, only differing in color^ ni the 

 greater length of the rostrum, iif the more swollen, elevated, and 

 laterally expanded brain case, and the shorter and broader interp- 

 terygoid fossa. 



