SCIURIDA—SCIUROPTERUS. 653 
GrENusS SCIUROPTERUS F. Cuvier 
Sciurus LINN2ZUS (in part), and of early authors generally. 
Pteromys G. CUVIER (in part), and of most recent authors. 
Sciuropterus F, Cuvier, Ann. du Mus, x, 1825, 126, pl. x (type, Sciurus volans Linn.); Dents des Mam- 
miféres, 1825, 162, 255. 
GevNERIC cHARS.—Skull short, broad, highly arched, in general form almost 
a miniature of that of Scewrus hudsonius; the supraorbital notch, however, is 
rather deeper, and the interorbital region is rather more constricted; the orbital 
fossee are relatively larger, as are also the auditory bulle and the ears, in 
conformity with the more nocturnal habits of the members of this group; 
the pterygoid processes are more slender, and posteriorly touch the auditory 
bull. In other particulars, the skulls of Sccwropterus and Sciurus present 
no important differences. Premolars two, the first minute, but reaches the 
plane of the trituration. Limbs united by a furred membrane formed by the 
expansion of the skin of the sides of the body, and supported anteriorly by 
a slender bone articulating with the carpus and directed backward. Tail 
two-thirds as long as the head and body together, broad and flat, the longer 
hairs being chiefly directed laterally, thus forming an important aid in govern- 
ing the direction of their flight-like leaps, as well as serving as a further 
means of support in their short flights from tree to tree. Sciuropterus is 
thus merely a modified form of Sciurus, possessing rudimentary powers of 
flight, through the support afforded by a parachute-like expansion of the skin 
of the sides of the body and the broad, flat tail. The pelage is dense, soft, 
and furry; the ears large and sparsely clothed; the colors some soft, dull 
shade of brown above and whitish beneath. Animals of small size, and of 
crepuscular or nocturnal habits. 
The genus is represented in North America by a single species of wide 
distribution, and presenting a very wide range of geographical variation in 
size. A single species also represents the genus in Europe, but several other 
commonly recognized species occur in Asia. The Sciuropterus volans of 
Europe differs from the American S. voduced/a in its much smaller size and 
relatively much shorter and smaller tail, as well as slightly also in color. 
The Flying Squirrels were first separated from ordinary Squirrels by G. 
Cuvier* in 1800, he then giving to the group of Flying Squirrels the generic 
name Pteromys. In 1825, his brother, F. Cuvier,t separated the small Flying 
*“Tecons d’anatomie comparée, i, 1800.” The original edition of this work I have been unable to 
consult. 
t Ann. du Mus., x, 1825, p. 126. See also Dents des Mammiferes, 1825, 162, 255. 
