28 NELSON 



Cranial characters. — Premolars \. Skull long and rather narrow ; 

 braincase inflated over interparietal region ; rostrum long, compressed 

 laterally ; nasals much longer than interorbital breadth, much narrowed 

 posteriorly and expanded anteriorly ; occiput high and narrow ; 

 squamosal process of zygomatic arch turning abruptly down, the arch 

 ascending more obliquely from back to front than m Hesperosciurus. 



General notes. — This subgenus includes S. carolinensis and its 

 subspecies of the eastern United States. It is an Austral and Tran- 

 sition zone group. Neosciurus is most closely related to Hespero- 

 sciurus., from which it is distinguished by the braincase, which is 

 highly arched over the interparietals and narrowed and rounded pos- 

 teriorly. These two groups balance one another in the eastern and 

 western United States much as do Parasciurus and Arceosciurus. 



OTOSCIURUS' subgen. nov. (p1. I, fig. 2). 



Type Sciurus a:3e"r// Woodhouse, from San Francisco Mt., Arizona. 



Distribution. — Rocky Mountains and Sierra Madre, from state of 

 Colorado to Durango, Mexico. Transition zone. 



External characters. — Ears long and broad, with magnificent 

 tufts in winter; tail short and unusually broad; feet very large. 

 Upperparts mainly gray ; underparts white, with lateral line more or 

 less distinctly black. 



Cranial characters. — Premolars \. Skull short and broad ; frontal 

 area flattened ; braincase depressed, inflated laterally; rostrum com- 

 pressed laterally, rather light ; nasals long (equalling interorbital 

 breadth) . 



General ?zotes. — Otosciurus like Tamiasciurus has strong ex- 

 ternal characters by which it may be at once recognized. The group 

 contains three species, S. aberti., S. coticolor., and S. durangi., which 

 range through the yellow pine forests of the Transition zone in the 

 southern Rocky Mountains and northern Sierra Madre. 



Subgenus TAMIASCIURUS Trouessart (p1. I, fig. 8). 



T'afniasciurzisTROUBSSART, Le Naturaliste, II, No. 37, Oct. iSSo, p. 



292; Cat. Mamm., Rodentia, pp. 81-82, 1880; Merriam, Proc. 



Biol. Soc. Washington, VII, p. 23, 1897; Allen, Bull. Am. Mus. 



Nat.^Hist., N. Y., X, pp. 249-298, 1898. 

 Macroxus Trouessart, Catalogus Mammalium, nov. ed., II, pp. 421— 



429, 1897 (part). 

 Type '•Sciurus hudsofzius Pall.' (=5'. hudsofiicus Erxl.), from 

 Hudson Bay. 



^ From ov-^ wrof , ear ; -|- Sciurus. 



