SQUIRRELS OF MEXICO AND CENTRAL AMERICA 29 



Distribution. — Most of the wooded parts of the United States and 

 British America ; south to northern Lower California, Mexico. Bo- 

 real and Transition zones. 



External characters. — Size small — under 450 mm. ; ears long, 

 well haired, conspicuously tufted in winter; tail short, bushy, flat- 

 tened ; lateral line (present in summer) black. 



Cranial characters. — Premolars \ sometimes \ (the first very small 

 and irregular in development) ; skull short, wide and depressed; ros- 

 trum short and stout ; nasals shorter than interorbital breadth ; anterior 

 end of zygomatic arch unusually broad and abruptly spreading; aud- 

 ital bullce proportionately large. 



General ?iotes. — Tamiasciurus was proposed by Trouessart in 1880 

 and subsequently dropped into synonymy until revived by Dr. Mer- 

 riam in 1S92. Curiously enough Trouessart reduced it again to 

 synonymy in 1S97, uniting it with most other North American squir- 

 rels under the untenable subgeneric name Macroxus. In 1898 Dr. 

 Allen again revived the subgenus, which is unquestionably worthy of 

 recognition as a well marked natural group. Tamiasciurus includes 

 all of the Chickarees, S. hudsonicus^ S. douglasi and S. fretnonti 

 with their subspecies. As already stated by Dr. Merriam, this sub- 

 genus is of Boreal origin, but is also common throughout a large part 

 of the Transition zone in the United States. 



AR^OSCIURUS^ subgen. nov. (p1. I, fig. 3). 



Type Sciurus oculatus Peters, from eastern Mexico. 



Distribution. — Mountains bordering the tableland of Mexico from 

 the volcanoes of Orizaba and Toluca north to central Arizona and 

 west-central New Mexico. Transition zone. 



Exter7ial characters. — Size large ; body rather slender ; tail usually 

 long, sometimes exceeding length of head and body ; upperparts gray 

 or yellowish ; underparts white or yellowish. 



Cranial characters. — Premolars \. Skull rather short, depressed ; 

 braincase broadened at parietals ; occiput low and broad ; front of 

 skull depressed at base of rostrum (more arched in Parasciurus) ; ros- 

 trum light ; nasals narrow, slightly tapering posteriorly ; upper end of 

 premaxill£e narrow. 



General 7iotes. — The subgenus Arceosciurus is characteristic of the 

 Transition zone in the mountains bordering the tableland of Mexico 

 from Mts. Orizaba and Toluca northward. It is intrusive in the United 



* From apaloq, slender ; -j- Sciurus. 



