RODENTIA ARVICOLINAE ARVICOLA TOWNSENDII. 527 



ABVICOLA TOWNSENDII, Bachman. 



Oregon Ground Mouse. 



Arvicola toumsendii, BACHMAN, J. A. N. Sc., Phila. VIII, i, 1839, 60. IB. In Townsend's Narrative, 1830, 315. 

 WAGNER, Wiegmann's Archiv, 1843, u, 53. 

 AUD. & BACH., N. Am. Quad. HI, 1853, 209 ; pi. cxliv, fig. 1. 



Sr. CH. Very large, (head and body 5 inches.) Ears 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 vertebrae 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 -j- 71, or as 100 : 56. 



This species is one of the largest of its genus in ^orth 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 

 vertebras ; 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 le&s 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 d^sky 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 (- 4 Tnr) 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 

 convexity 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 



