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PTEROMYS ALPINU S.— A u d. and Bach. 
Rocky Mountain Flying-Squirrel. 
PLATE CXLIII .—Fig. 2.— Natural Size. 
P. Magnitudine P. sabrino major, cauda pland, lata, corpore longiore, 
patagio lumbari angusto, margine recta. 
CHARACTERS. 
Larger than Pteromys sabrinus ; tail, flat and broad, longer than the body J 
flying membrane, short and with a straight border. 
SYNONYME. 
Pteromys Sabrinus (Var. Alpinus). Rich., F. B. A., p. 195, pi. 18. 
DESCRIPTION. 
Head longer and body stouter than in P. sabrinus ; the tail is also 
longer, much broader, more densely clothed with hair, and has a flatter 
and more elliptical form ; the flying membrane is much smaller than in P. 
sabrinus, and the border is straight ; the ears are thin and membranous, 
have a little fur at the base on the upper surface, and are thinly covered 
on both sides with short adpressed hairs ; their form is semi-oval with 
rounded tips ; the tail is flat, oblong, and oval in form ; the extremities 
are rather stout, more especially the hind-feet ; the soles, palms, and under 
surfaces of the toes are well covered with fur, except a small callous emi- 
nence at the end of each toe. There are five eminences on the palm, of 
which the two posterior ones are the largest ; and four on the soles, situated 
at the root of the toes. There is a brush of soft fur near the outer edges 
of the soles ; the fur is dense, very long, and has a woolly appearance ; the 
longest hair on the back is fully an inch in length. 
COLOUR. 
Head, nose, and cheeks, light grayish, with a slight wash of yellow ; 
surface of the fur on the back, yellowish brown, without any tendency -to 
the more red hue of the back in P. sabrinus. 
