5386 U. Ss. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
length of the hind feet is a little less than .7 ; the longest toe, .23; the tail is about an inch 
long, well covered with hair. The fur is long and loose, the under hair measuring .4 of*an 
inch. - Much longer hairs are thickly interspersed ; some are .55. 
The specimen described appears almost black, its general tint is so dark. The hairs, how- 
ever, on the back and sides have short tips of grayish brown, barely with a pale fulvous tinge, 
most conspicuous along the side of the head. The under parts are dark lead color, with a hoary 
gray tinge caused by the colored tips being hoary, the general impressing being a plumbeous 
hoary. The line of separation between the colors of the sides and belly is appreciable, but not 
distinct. The tail is dark brown above, plumbeous hoary beneath. The feet are dark brown. 
The posterior upper molar has one anterior triangle, one interior, and two exterior, besides 
an unusually long posterior bent crescent which occupies nearly half the tooth. The posterior 
outer triangle, however, is very small, and rests on the curve of the crescent. The crescent 
sends forth a supplementary lobe from its inner side. There are four salient angles on the 
inside of the tooth, besides the posterior loop of the crescent, which may be called a fifth, and 
three exterior ones, besides the convexity of the crescent. The anterior lower molar has one 
posterior triangle, three exterior, and three interior; the anterior trefoil thus has its external 
loop converted into a closed triangle, the anterior loop and inner lateral one opening broadly into 
each other. There are five interior salient angles, besides a partial one produced by the bending 
in of the anterior loop. The exterior angles are four, besides the convexity of the anterior 
loop. 
A still younger Arvicola (593) was brought from the same locality, Sawatch Pass, and is 
probably distinct, although too immature to characterize with any safety. The feet and tail 
are shorter in proportion. The ears are similar, and also concealed beneath the skin. The 
upper parts and sides have a clear uniform wash of yellowish rufous, with a slight mixture of 
black, which scarcely obscures the color. The belly is an ashy white, showing the plumbeous 
base of the fur. The feet are brown; the tail brown above and white beneath. 
List of specimens. 
= Measurements. 
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594 | 1717 | Sawatch Pass, R. Mts..| Capt. Beckwith....| 16 | Skin.... 2.75 -90} 1.00} .40| .70) .23 22 .35 Mr. Kreutzfeldt.. 
| 
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