528 U. Ss. 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 Jower 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. 7 
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. 
= | Measurements. 
3 | . ; 
= ca Locality. When Whence and how 5 | 3 Pls = BS = |; | Collected by— 
BIS | ¢ collected. obtained. Ell lsls|/s/8l)e/sl/2/2 
& |s3 | 3 | «a elalo (= l/Hl/sjlel; ule 
o |& s i we ‘Ss = e Se 1 = je hee pa, 
5 ois =| °e SAO [eo Sey es S| PR las 
0 mls S ° 2 ra HY Ae EEE | HS = 
a a N=[) (c= fee Wossie|(eee ty ecclesia (eed =e Wee ce 
Sele Be eS) Siig | | eee ie is 
S 2 - o os 2 | 
6 |S | a S| 4 lalelaelaialalzlalé 
| aan a | oa (a | [7 =o 
464* 1595),...| Shoalwater bay .-....+0000- TESA es sees Gov. I. I. Stevens... sees Skin. '5,502,00/2.95) .62/1.02) .34 -71, Dr. J. G. Cooper. 
580 |eocsleseclcccoee do Sept. 1854..) Dr. J. G. Cooper....| 19 + do .- 5.00 2.00)2.25 -60)1,02) .33 ee 
1382? . Q secees do ane Aug. 1855..}...008 dO. secccccene| seve |,.do ../5.002.00/2.20) .59)1.00) .32 «| 
| 
2396 sees leeee Puget’s Sound, ...e.+eeeee 1856... esas Dr. G. Suckley. ...| .../.. do «.|6.00}....|2.00)....Jesseleseel.oo- tees leeee, 
1275 3235 ....| Crater Pass, Cascade Moun-| 1855....... Lt. R. S.Williamson}.... ..d0../5.25)1.75/2.00) .60)1.01) .35 -68 Dr. J. S. New- 
tains. | bery. 
2 When fresh this specimen measured 7§ inches with the tail; the ear } of an inch in length by } an inch in breadth. The iris was black, 
* When fresh this specimen measured to root of tail 5.50 inches; tail, 2.50; hind foot, 1.00; fore foot, .50; (?) ears, .60, 
ARVICOLA MONTANA, Peale. 
Arvicola montana, Prare, Mamm. & Birds of U. 8. Ex. Ex. 1848, 44. 
Aup. & Bacn. N. Am. Quad. III, 1854, 302. 
Sp. Cu.—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 aninch, ‘Tail long; about 
two-fifths of the head and body; vertebre 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 skull. . 
1269. This species is about the size of the largest of the Arvicola found in the Atlantic States, 
but is considerably less than the 4. townsendii. The body is stout and full; the hair rather 
