SQUIRRELS OF MEXICO AND CENTRAL AMERICA 29 



Distribtdion. — 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 bullae proportionately large. 



General notes. — Tainiaschirus was proposed by Trouessart in 1880 

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

 riam in 1892. Curiously enough Trouessart reduced it again to 

 synonymy in 1897, 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. 



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



Type Sciurus oculatiis 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. 



External characters.— '^\-lq\2^x^Q\ body rather slender; tail usually 

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

 or yellowish ; underparts white or yellowish. 



Cranial characters.— Yx^moXax^ \. 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 

 premaxillte narrow. 



General notes— ThQ 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 



1 From apaloq, slender ; + Scitirus. 



