170 Bulletin American Museum of Natural History. [Vol. XXXIV, 
genera recognized by Nelson in 1899 being suppressed, and Sciwrus retained 
in a generic sense for all the species except those referred to Microsciurus and 
Syntheosciurus, which were accepted as full genera. 
As noted by Nelson, the subgenera recognized by him in 1899 “occupy 
clearly defined geographic areas and, without exception, the ranges of the 
most closely related groups are separated by a distinct gap”’ (/. c., p. 24). 
Tamiasciurus is the most northern group, occupying the wooded temperate 
and cold temperate parts of North America, no member of the group 
occurring south of the 34th degree of latitude except in the higher mountain 
ranges. Neosciurus is restricted to the eastern half of the United States, 
nowhere reaching the Mexican border. Hesperosciurus is its representative 
on the west coast, where it occurs, chiefly in the mountain ranges, from 
western Washington to northern Lower California, its range slightly over- 
lapping that of Tamiasciwrus, with which it has no near genetic relationship. 
Otosciurus is restricted to the southern Rocky Mountains and the northern 
Sierra Madre of northern Mexico. Parasciwrus is limited to the eastern 
United States, ranging (formerly) from central New York to Texas and the 
immediately adjoining portions of northeastern Mexico. Ar@osciurus 
inhabits the mountains bordering the tableland of Mexico from about 
6000 to 12,000 feet, and extends north into southwestern New Mexico and 
southern Arizona, and south to Pueblo and western Vera Cruz. The 
ranges of Parasciurus and Ar@osciurus nearly meet in northeastern Mexico; 
while-some of the forms differ slightly in cranial characters, Arcosciurus 
may well be united with Parasciurus. 
The preceding six groups are warm temperate to boreal in their geograph- 
ical ranges, while the following four are tropical. Echinosciurus ranges 
from southern Mexico south to Costa Rica and Panama, but does not 
extend into South America. It comprises all the large squirrels (some 50 
species and subspecies) of this extensive and greatly diversified area. Baio- 
sciurus is also tropical, ranging from central Tamaulipas through eastern 
Mexico to Nicaragua. Guerlinguetus (as recognized by Nelson, not Guerlin- 
guetus Miller) is chiefly South American in its range, but extends north to 
northeastern Nicaragua. Microsciurus ranges from central Costa Rica 
south in the Andean region to Peru. Syntheosciurus is known only from 
the mountains of Chiriqui. 
1 These 96 forms (38 species and 58 additional subspecies) were distributed as follows: 
Subgenus Tamiasciurus, 21 forms, referred to 3 species. 
Subgenus Baiosciurus, 4 forms, referred to 2 species. 
Genus Sciurus (= Echinosciurus, Neosciurus, Hesperosciurus, Otosciurus), 50 forms, 
_ referred to 20 species. — 
Subgenus Guerlinguetus, 16 forms, referred to 9 species. 
Genus Microsciurus, 4 forms, referred to 2 species. 
Genus Syntheosciurus, 1 form. 
