140 



Nelson . 



Species o/ Arvicola. 



which incloses the base of this member below. The feet and 

 legs are dull whitish. The fur is long and very soft, except on 

 the tail. The tail hairs are rather coarse and stiff and the termi- 

 nal pencil is peculiarly bristly with a length of 6 mm. 



The ears are rounded and clothed on the inner side of conch 

 by yellow hairs. They are wholly concealed by the fur. 



The under fur, with basal two-thirds of the 

 long hairs, is of a uniform dark slaty color ; 

 succeeding the dark base the majority of the 

 long hairs of the back have a plain fulvous tip. 

 The tips of the longest hairs, however, are 

 black, succeeding a yellowish zone, thus pro- 

 ducing a slight wash of darker over the back. 



A slight variation in color is apparent among 

 the specimens, due to the varying intensity of 

 the fulvous. The soles of feet are naked. 

 The thumb nail is short, stout, and spatulate 

 and does not extend beyond end of the thumb. 

 Dentition. The accompanying figure shows 

 the pattern of the crowns of the molar teeth. 

 Skull measurements of five specimens of Arvicola operarius 

 from St. Michaels, Alaska : 



b a 



Molar teeth of Arvi 

 cola operarius x 5. 



a, upper; 6, lower. 



The present species may be readily distinguished from any 

 known American Arvicola by its smaller size and pale fulvous 

 color. It is very abundant along the coast tundras of Bering 

 Sea from Cape Vancouver north at least to Bering Straits, in- 

 cluding Nelson, St. Michaels, and Stewart Islands. It makes 

 numerous runways through the moss and under the grass in all 

 the tundra districts where it lives, and as winter approaches 

 gathers stores of small bulbous roots, sometimes placing a peck 

 or more in a single cavity just below the surface on a mossy 

 knoll or slope. 



