RODENTIA—ARVICOLINAE—ARVICOLA TOWNSENDII. 527 
ARVICOLA TOWNSENDII, Bachman. 
Oregon Ground Mouse. 
Arvicola townsendii, Bacuman, J. A. N. Sc., Phila. VIII, 1, 1839, 60.—Is. In Townsend’s Narrative, 1830, 315. 
Waaner, Wiegmann’s Archiv, 1843, 11, 53. 
- Aup. & Baou., N. Am. Quad. III, 1853, 209; pl. cxliv, fig. 1. 
Sr. Cu.—Very large, (head and body 5} inches.) ars large; two-thirds as long as hind foot; well furred. Tail, in- 
cluding the hairs, rather less than half the head and body ; the tail vertebra twice the length of hind foot. Thumb claw 
conspicuous. Toes long; one-third the whole foot. Fur measuring a little over one-third of an inch, with a slight gloss, 
Above, dark fuscous brown, with but little yellowish brown visible. Sides paler; beneath, ashy white. Tail almost 
uniformly brown throughout, Feet liver brown. Skull, 1.27 + 71, or as 100 : 56. 
This species is one of the largest of its genus in North America, perhaps the largest of those 
occurring in the United States, though less than the Arvicola amphibia of Europe. The head 
is broad and blunt ; the whiskers are as long as the head; some black, the others light gray. 
The ears are quite unusually large and broad ; .62 of an inch, or nearly two-thirds as long as 
the hind foot, (1.02 inches.) They are well covered with hair on both surfaces, except around 
the meatus, and project about an eighth of an inch beyond the fur when laid back flat. 
The feet are large; the anterior, measured from the carpal joint, as long as the ear, (.62 of an 
inch.) The thumb is short, and armed with a small claw with the point worn off; the third 
claw is longest, the fourth a little shorter ; the second claw reaches a little beyond the base of 
the third ; the fifth is shorter than the second. The hind foot is about half as long as the tail 
vertebra ; the sole is hairy from the heel to the tubercles; the toes are long; the middle one 
equalling half the rest of the foot. The first claw reaches to the notch between the second and 
third toes ; the third toe is a little longer than the second and fourth; the fifth claw scarcely 
reaches the base of the fourth. 
The tail is long ; with the hair, it is a little less than half the head and body in- the dried 
skin. It is covered with short stiff appressed hairs of nearly equal length throughout, and ter- 
minated at tip by a scanty pencil. The hairs on the body are rather coarse, and measure a 
little over one-third of an inch above. There is a slight gloss to the fur. 
There is nothing in the coloring of this species which distinguishes it specially from others of 
the genus in the east ; the prevailing color above being a yellowish rusty brown, so much over- 
laid with black hairs as more or less to conceal it, especially along the back. The sides are 
paler, with much less black. The cheeks are a shade brighter than the sides. The under parts 
are dirty ashy white, with a very obscure wash of light brownish. The feet are pale liver 
brown. The tail is. dark brown above, passing insensibly into a little paler shade beneath, 
There is a dusky tinge on the side of the nose, and the edges of the lips are white. One speci- 
men (1382) has the under parts tinged with a very pale dirty yellowish brown. 
A skull of this species (+,°°°) is larger than that of any North American species with which 
I am acquainted, measuring 1.27 inches by .71, and .4 from the molars to the incisors. The 
occipital foramen is higher than broad, with a distinct emargination above. The middle upper 
molar has but four triangles, the posterior having merely an inner heel, giving it a quadri- 
lateral shape. The posterior upper molar is composed of one complete triangle anteriorly, one 
interior, and two exterior. The posterior portion is composed of a closed crescent, with the 
ecnvexity exterior, and a spur on the inner face. The posterior loop of the crescent, however, 
is not an internal salient angle, but a posterior ; its inner side, however, is concave. There 
