656 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
SPECIFIC CHARS.—Size varying greatly with locality. THead and body 
ranging, in adults, from 7.50 to 4.75 inches; tail-vertebrae from 5.00 (or a 
little more) to 3.59; tail, with hairs, from about 6.50 to 4.25 (occasionally 
less). Above yellowish-brown, varying to pale reddish-brown; below white, 
varying to creamy-white, with sometimes a faint tinge of pale rufous; tail 
above generally darker than the back, especially at northern localities, where 
it is sometimes decidedly blackish; tail below lighter than above, varying 
with locality from dusky-brown to yellowish-brown, always more strongly 
colored than the ventral surface of the body. 
Var. HUDSONIUS. 
Northern Flying Squirrel. 
VARIETAL cHARS.—Length, exclusive of the tail, 6.00 inches or more; 
tail, with the hairs about 5.00. Above dull yellowish- or reddish-brown; 
below white, faintly washed with yellowish; tail above dusky, often decidedly 
blackish on the edges and terminal half; also frequently dusky toward the 
end below. Habitat mostly north of the parallel of 49°, extending further 
southward along the Rocky Mountains and on the Pacific slope. Grades 
insensibly into— 
Var. VOLUCELLA. 
Southern Flying Squirrel. 
VARIETAL CHARS.—Similar to the preceding, but much smaller. Length, 
exclusive of the tail, less than 6.00 inches; generally less than 5.50. Tail 
Jess dusky, often with no blackish whatever, and the general color of the 
body above rather more yellowish. Habitat, United States,—exclusive of 
the Pacific slope north of California, and the Rocky Mountains north of Col- 
orado ; and thence southward to Guatemala. 
The American Flying Squirrels present a range of geographical varia- 
tion in size quite unparalleled in other members of the Sciuride, and only 
equalled in some species of the Canidae, and possibly in Cervus virginianus. 
On the other hand, the coloration is remarkably constant, almost exception- 
ally so, no other North American Mammal with which I am acquainted, 
which has so wide a geographical range, varying so little in this respect with 
locality. The species ranges from Arctic America into the tropical portions 
of the continent. I have specimens before me from points as distant as 
