518 U. S. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
ARVICOLA (HYPUDAEUS) GAPPERI, Vigors. 
Arvicola gapperi, Vicors, Zool. Jour. V, June, 1830, 204; pl. ix.—(Canada.) 
Dexary, N. Y. Zool. I, 1842, 91. 
Scuinz, Syn. Mam. II, 1845, 252. 
? Arvicola fulva, Aup. & Bacu. J. A. N. Se. VIII, m1, 1842, 295. 
2 Arvicola dekayi, Aup. & Bacu. N. Am. Quad. III, 1854, 287. 
Sp. Cu.—Size small and slender, about like that of the domestic mouse (33 inches long.) Skull about .9 of an inch. Ear 
large, two-thirds the hind foot; prominent above the fur; well and closely furred, with short hair. Antitragus large. Tail 
vertebra about twice as long as the hind foot. Back with a broad stripe of uniform bright rufous brown ; sides sharply defined 
yellowish gray, mixed with brown; muzzle similar; beneath, dull yellowish white. Tail sharply bicolor, grayish and black 
mixed above, whitish beneath, dusky at the tip. 
This species is of small size and of slender form compared with the others found in the northern 
and eastern States. The proportions are those of the house mouse, but the size is rather larger 
or about that of the white-footed mouse of the northern States. 
The hair is soft and full, but rather short, measuring about .35 of an inch above and half as 
much below. The head is rather pointed, at least in the dried skins. The whiskers are as 
long as the head; black and grayish white. The eye is rather large, and appears situated 
nearer the nose than the ears. The ear is large, longer than wide, and clearly visible beyond 
the fur at all times, which it usually exceeds by nearly a quarter of an inch. Its length is more 
than two-thirds that of the hind foot. It is uniformly and densely coated on both sides with 
short hairs, and has almost the finish of a squirrel’s ear, thus differing much from the common 
northern species. There isa large, nearly semi-circular antitragus, apparently capable of closing 
the meatus. 
The feet are rather short, slender, and weak, the anterior long in proportion to the posterior, 
being more than half the length. There is a short, blunt claw enveloping the rudimentary 
thumb. The sole is covered with close fine hair from the heel to the tubercles, or for a little 
more than one-third ; there is also some hair growing over the edge of the sole anterior to this 
point. The tail is long; the vertebra about twice as long as the hind foot, though the pro- 
portion varies in specimens; it is also rather more than one-third the head and body. It is 
well covered with stiff appressed hairs, a little longer towards the tip, and at the tip forming 
a pencil.! 
The prevailing color of the upper parts is a lively uniform rufous or chestnut brown; the 
color commencing on the crown and passing backwards in a well defined dorsal stripe about the 
width of the head. The sides and anterior of muzzle are pale brownish gray, with a tinge of 
yellowish; the color well defined against the dorsal stripe, but passing rather insensibly into 
the yellowish grayish white of the under parts. The sides of the muzzle are like the belly. 
There are numerous longer fine hairs interspersed among the fur of the back of a dark reddish 
brown or clear brown color ; but these do not obscure the brighter tints. The feet are grayish 
white. The tail above mixed grayish and brown; darker and almost black near and at the 
tip. The under parts are like the belly. 
There are slight variations in the color of different specimens, the above description being 
1 The following notes are derived from a specimen in alcohol: This animal is much more like the long-tailed mice in ex- 
ternal form than the Arvicolae. ihe ears are large and prominent, the membrane thin, and not inflected at its anterior edge. 
The antitragus is well developed into a valve. ‘The muzzle is quite acute, almost as much as in the mice ; the whiskers are full 
and long. The feet are slender, and not very long ; the soles have six tubercles, the posterior inner rather small. 
