RODENTIA—-SCIURINAE-—PTEROMYS VOLUCELLA. 
287 
Pteromys volueeUa, Yarrell, Pr, Comm. Science Zool. Soc. London, I, 1830, 38. (Anatomy.) 
Dekay, N. Y. Zoology, I, 1842, 65; pi. xvi, fig. 2. 
Wagner, Supplement Schreber, III, 1843, 231. 
Aim. & Bachman, N. Am. Quad. I, 1849, 216 ; pi. xxviii. 
Kennicott, Rep. Pat. Office, 1856, Agricultural, (1857,) 69 ; pi. vii. 
‘ 1 Sciuroptems volucella, Geoffroy, Diet. Class XIV, 132.” 
VtSciurus acrobates, (Linn,) Schreber, Saugt. IV; tab. ccxxii, B. no text 
Flying squirrel, Pennant, Hist. Quad. 1781, Ho. 283.— Ib. Arctic Zoology, 1784, 120. 
Assapan, St. Hilaire, and Cuvier, Hist, des Mammif. Ill, 1819 ; plate. 
Sp. Ch. —Tail, with hairs, nearly as long as the head and body. Above light yellowish brown ; the tail similarly colored, 
or with a more smoke-colored tinge. Beneath creamy white, the hairs white to the. roots ; under surface of tail more red¬ 
dish. Length of head and body about 5 inches ; of tail, with hairs, half an inch less ; hind feet 1. 20 inch. 
The ears of this species are large and broad ; much thinner and more ample than in the 
ordinary squirrels. Their concavity is nearly naked ; the back is covered with very short hairs. 
The head is short, broad and depressed. The muffle is entirely hairy, except on the septum 
and the extreme edge of the nostrils, which are naked. The upper lip is deeply cleft,' the 
fissure extending to the nose, and continued on the septum as a groove. The whiskers are very 
long, and extend as far as the axillae. 
The feet are only moderately large; the first fore finger is very rudimentary, in fact apparently 
wanting; nor have I been able in preserved specimens to detect the presence of a nail or claw. 
The other four fingers are very deeply cleft, so much so that they occupy rather more than one- 
half of the total length of the hand from the wrist. The central two fingers are longest and 
equal; the fifth claw reaches to the base of the fourth ; the second finger is a little shorter than 
the fifth. The hind toes are long, but less so in proportion than the anterior ones. The palms 
are naked ; the soles densely hairy from the heel to the large tubercles at the bases of the toes ; 
in some cases even the under surfaces of the toes appear more or less hairy. The claws, the 
anterior especially, are excessively short and much curved. The lateral membrane is supported 
anteriorly by a bony process articulated to the wrist, and extending backwards, slightly 
divergent, from the fore arm; it is longer than the hand, and but little shorter than the 
foot, (.82 in 2309.) This bony process is freely articulated with the wrist, and is capable of so 
extending or stretching out the flying membrane, that when at nearly a right angle with the 
hand it carries the anterior edge of the membrane with it at the same angle ; and then the 
anterior portion of the lateral edge will be at right angles with the anterior edge proper, and be 
parallel with the arm. In this event such a prominent angle of the membrane will be produced 
as is described as characteristic of Pteromys oregonensis, as distinguished from other species. If 
not artificially stretched out, as appears to have been done with Townsend’s specimen of the last- 
mentioned species, the process lies flat to the arm, and then the membrane appears to start from 
the wrist, and extends along the side of the body with little or no appreciable angle. 
The tail is very much flattened, though broad, and about the width of the head. The hairs 
are arranged on either side somewhat like the flumes of a pen. 
The fur of this animal is exceedingly soft and silky ; the upper parts are of a light yellowish 
brown ; the tail is quite'similar, with perhaps more of a light smoky tint; the hair is of nearly 
the same color from the roots ; the hairs of the back are dark brown, excepting at the tip ; the 
under parts are of a creamy white ; the tail, with a grayish rusty tinge, the hairs white to the 
roots. The sides of the head are grayish ; of the muzzle and cheeks whitish ; there is a suffu¬ 
sion of darker round the eyes. 
This species appears to vary somewhat in size, though but little in color. Specimens from 
the south are darker above, and the tail has rather a rusty tinge. 
