RODENTIA ARVICOLINAE ARVJCOLA CALIFORNICA. 533 



belly grayish white, the colors passing quite insensibly into each other. Tail bicolor, upper 

 and lower surfaces not distinctly separated. Skull, 1.14 by .65, or 100 : 57. 



This animal in size nearly equals the larger species of the Atlantic States, and is provided 

 with soft and unusually long fur, measuring nearly six-tenths of an inch above. The whiskers 

 are as long as the heed, and grayish white in color. The ears are rather large, and scarcely 

 concealed beneath the fur, about five-eighths as long as the hind foot ; they are well covered 

 with long hairs on both sides, except about the meatus, and have a distinct segmental anti- 

 tragus. The feet are broad and stout, the hinder rather short, the anterior a little more than 

 half as long as the posterior. The thumb of the hand is obsolete, and its place indicated by a 

 blunt claw. The tail is moderate, about twice as long as the hind feet, tapering considerably, 

 and uniformly coated with appressed hairs to the pencilled tip. 



The prevailing color above is lustrous, light yellowish brown, varied with the black or dark 

 rufous brown points of the longer hairs. These do not obscure the ground color much, however, 

 leaving the general tint a yellow brown or brownish reddish yellow. The sides are rather 

 paler. The under parts are grayish white with a yellow tinge, due, perhaps, to alcohol. The 

 feet above are brownish gray ; the tail is dark brown above, passing insensibly into a paler 

 beneath. The feet ai-d tail have a rufous tinge, in addition to the colors described. 



Skull. The skull of this species is large and broad ; the width about 57 hundredths of the 

 length. The muzzle is long in proportion, and the narrow interorbital portion of the frontal 

 bone widens out behind at a point about midway between the end of the nose and the occiput., 

 instead of being considerably forward of this point, as in A. occidentals. The anterior extremity 

 of the upper molars is distant from the posterior face of the incisors one-third the distance from 

 the incisors to the occiput. 



The posterior upper molar has one anterior triangle, two exterior and one interior, besides 

 the posterior bent crescent. This sends out a short lobe outwards near its posterior portion or 

 bend, a character rarely observed in American Arvicolae. We have thus, instead of three 

 external salient angles with a rounded space behind them, this last mentioned space indented 

 by a shallow furrow, so as to produce two short, blunt salient angles, making five external in 

 all. The anterior upper molar has one posterior triangle, three interior, two exterior, and an 

 anterior tri-lobed trefoil, the lateral exterior lobe of which is produced backwards to form nearly 

 as decided a salient angle as the three behind it. There are thus four external salient angles 

 and five internal, besides the sub-angular anterior loop of the trefoil. 



Measurements. 



