538 



U. S. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



The only American species with which this Arvicola need toe compared are those of which A. 

 pinetorum is the type. From these, however, it differs not only in its much darker color, but 

 by the large, more orbicular and naked ears, smaller fore feet, larger hind feet. The fore claws, 

 also, are not longer than the hind. The differences in the skull are considerable. 



A specimen in alcohol, from Steilacoom, received since the preceding description was prepared, 

 is, in size, much as described. The ears are low, orbicular, the membrane thickened, the mar 

 gins or conchal portion much inflected or incurved, like a half open apple blossom, the concha 

 being inflected all round. The antitragus is well developed, but rather low. The surfaces of 

 the ear appear perfectly naked, with, however, a ciliation of long hairs towards the roots of the 

 concha, on the dorsal surface. A close examination of the auricle in the dried specimen shows 

 a few scattered, very short, white hairs. 



The structure of the ear, though in many respects similar to that of A. pinetorum) is yet 

 essentially different. Thus the upper and lower roots of the margin of the ear meet anteriorly 

 go as to form even a low rim to the meatus anteriorly, completely enclosing the aperture ; the 

 edge of the concha is inflected ; the region inside the auricle, around the meatus, naked, and the 

 antitragus so much developed as to be capable of completely. closing the meatus. In A. pine 

 torum the roots of the upper and lower margins of the ear are widely separated, by a space of a 

 quarter of an inch, the space between these roots and anterior to the meatus perfectly plane ; 

 the edges of the concha, or of the auricle, not inflected at all ; the inner space around the meatus 

 partly hairy ; the antitragus very slightly developed, not valvular, nor capable of closing the 

 meatus at all. 



The eyes are very small ; about as in A. pinetorum. The feet, also, resemble that species ; 

 the sole is hairy from the heel to the first toe. 



An alcoholic specimen from Tomales Bay agrees with this in nearly all respects, except that 

 the ear is smaller, and, though nearly naked, has a few long hairs on the inside of the ear, just 

 within the concha. 



I cannot make out the character of the tubercles on the soles of the Steilacoom specimen ; in 

 that from Tomales Bay there are but five, as in A. pinetorum ; a sixth may be present, but it is 

 very rudimentary. 



List of specimens. 



1 Length of body before skinning, 3.60 ; of tail, 1.13. 



