482 
MAMMALIA. 
to the season, having a summer and winter coat. In Sweden, 
Russia, and Siberia, it becomes of a fine greyish slate colour 
under the influence of cold. Its fur at this period acquires value, 
and is exported in considerable quantities. 
Genera Sciuropterus, Pteromys, and Anomalurus . — The animals 
divided into these three genera are vulgarly known by the name 
of Flying Squirrels. Their common character consists in their 
being provided with wing-like membranes, extending along the 
flanks between the anterior and posterior members. These 
membranes are covered with hair like the other parts of the body, 
Fig. 207. — American Jb'lying Squirrels {Sciuropter us volmella). 
and constitute veritable parachutes, which enable them to sustain 
themselves a little longer in mid-air than the commonalty of 
animals, and consequently to clear considerable distances at a 
single bound. 
These, then, are not wings, and of no use for ascent like the 
wings of Birds, but are only serviceable in descending and 
moving horizontally. With the exception of this characteristic 
feature, these three genera of Rodents have absolutely the 
physiognomy and the habits of the true Squirrels. 
The Sciuropteres (Winged Squirrels), Fig. 207, are the smallest 
of the flying Squirrels. They inhabit the northern regions of the 
globe, particularly Russia, Siberia, and North America; and it 
