536 



U. S. 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 h^iir measuring .4 of an 

 inch. Much longer lairs are thickly interspersed ; some are .55. 



The specimen described appears almost black, its general tint is so dark. The hairs, how- 

 over, on the back and sides have short tips of grayish brown, barely wit!i 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, b3sides 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, th,-ee 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. 



