528 



U. S. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



are thus three exterior salient angles besides the long curve, and four interior besides the pos 

 terior rounded point. The anterior lower molar exhibits four salient angles on each side, and 

 an angular lobe which almost presents a fifth external salient angle. There is one posterior 

 closed triangle, three exterior, and three interior. The anterior lobe is connected with the 

 adjacent interior salient angle, but not the exterior. The middle molar is scarcely narrower 

 than the anterior. 



The skin 1275, from Crater Pass, differs in having the upper parts more dusky, and the 

 line of separation between the colors of the sides and belly more distinct. There is also a dis 

 tinct light tinge along the sides just above this line. The skull varies a little in having a 

 simple crescent at the posterior extremity of the last upper molar, and only two external tri 

 angles in the anterior lower molar ; the trefoil having both lateral lobes. 



No. 1270, from the Upper Des Chutes, approaches near 1275, but is too young to determine 

 with accuracy. I have preferred referring it to A. montana. 



This species was first described by Bachman from specimens brought from Oregon by Town- 

 send. I am unable to speak of its relationships to the large Arvicola from the British territory, 

 described by Richardson. 



List of specimens. 



1 When fresh this specimen measured 7f inches with the tail ; the car { of an inch in length by i an inch in breadth. The iris was black. 

 ' When fresh this specimen measured to root of tail 5.50 inches ; tail, 2.50 ; bind foot, 1 .00 ; fore foot, .50 ; (?) ears, .50. 



ARVICOLA MONTANA, Peale. 



Arvicola montana, PEALK, Mamm. & Birds of U. S. Ex. Ex. 1848, 41. 

 ADD. & BACH. N. Am. Quad. Ill, 1854, 302. 



Sr. CH. Size of A. riparia, or a little less, (4.75 inches.) Fur about half an inch long. Ears short, as long as fore foot, 

 about half the hinder; sparsely coated with longish hairs. Feet short; hinder ones .80 of an inch. Tail long; about 

 two-fifths of the head and body ; vertebrae more than twice as long as the hind foot. 



Above, dull yellowish brown, uniformly and equally mixed with black ; lighter on the sides ; beneath, dull whitish ash. 

 No rusty tints. Tail distinctly bicolor. 



Skull, 1.12 -|- .62, or as 100 : 56. Distance between upper molars and incisors less than one-third the whole length of 

 the bkull 



1269. This species is about the size of the largest of the Arvicola found in the Atlantic States, 

 but is considerably less than the A. townsendii. The body is stout and full ; the hair rather 



