RODENTIA ARVICOLIKTAE ARVICOLA EDAX. 



531 



inch. The tail, in the dried specimen, is about two-fifths the length of the body ; it is well 

 covered with hair and has a scanty pencil at the tip. 



The upper parts in this species are of a dark dull yellowish chestnut, or rufous brown, mixed 

 with black ; no indication of rusty, however. The under parts are dirty whitish ash. The feet 

 are light brown ; the tail brown ; slightly paler at the base beneath. The line of separation 

 between the colors of the sides and belly is rather distinct. 



Skull. The skull belonging to skin 1268 has some striking peculiarities, which distinguish 

 it from others with which it has been compared. It measures 1.08 inch by .61 (100:55.) The 

 most prominent feature is the length of the skull anterior to the molars. Thus the distance 

 from the molars to the base of the incisors (.37) is considerably more than one-third that from 

 the incisors to occiput, or even rather more than one-third the length of the entire skull. The 

 molars are thus thrown further back than in other species. The line of upper molars measures 

 .24 of an inch, or less than one-fourth the length of the skull. 



The posterior upper molar has three exterior salient angles besides the posterior bent crescentic 

 lobe, which is without any supplementary loop on its inner side. On the inside there are 

 three salient angles, in addition to that of the posterior branch of the loop, or one anterior 

 triangle, two exterior, one interior, and a posterior crescent, with two loops, both pointing to 

 the inner side of the tooth. The anterior lower molar has one posterior triangle, three internal, 

 two external, and an anterior trefoil lobe, the lateral loops of which are somewhat reduced. 



This species differs from A. townsendii in the smaller size and the proportionally less feet 

 and ears, while it approximates to it in color. From A. edax its color and the smaller feet and 

 ears will distinguish it. It is of a darker and more rufous color than A. edax and montana,(?) 

 while its wider head and longer muzzle separate it from the latter, which it otherwise resembles 

 in the small feet and ears. The feet are still smaller, however, than in the A. montana. 



List of specimens. 



ARVICOLA EDAX, Leconte. 



California Ground Mouse. 



Arvicola edax, LECONTE, Pr. A. N. Sc. Phila. VI, 1853, 405. 



AUD. & BACH. N. Am. Quad. Ill, 1854, 270 ; pi. cliv, fig. 2. 



Sp. CH. Size moderate (head and body four inches ;) less than A. riparia. Ears large, longer than the fore feet; as long 

 as hind feet, minus the toes ; well furred. Tail about two-fifths of head and body, little over one and a half times as long as 

 hind foot. Hind foot .9 inch ; toes long. Color above, pale dull yellowish brown, without any rufous ; uniformly sprinkled 

 with black. Beneath grayish white. Tail strongly bicolor. Feet grayish white. 



The fur of this species is loose and harsh, not lying compactly, and without gloss. The hairs 



