538 
IT. S. P. R. R. EXP. AND SURVEYS-ZOOLOGY-GENERAL REPORT. 
The only American species with which this Arvicola need he compared are those of which A. 
pinetorum is the type. From these, however, it differs not only in its much darker color, hut 
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 
so 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 Steilaooom 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. 
Catalogue number. 
Corresponding number of 
skull. 
Sex and age. 
Locality. 
When collected. 
Whence and how 
obtained. 
Nature of specimen. I 
Measurements. 
Nose to eye. 
Nose to ear. 
Nose to occiput. 
Nose to tail. 
Tail to end of vert. 
Tail to end of hairs. 
Fore foot, length. | 
Hind foot, length, j 
i Skull, length. 
| Skull, width. 
j Height of ear. 
1383 1 
3232 
Shoalvvater B<ay, W. T... 
Aug. 1855 
Dr. .T. d. Cooper. 
Skin 
. 3.50 
1.10 
1.25 
.38 
.65 
.92 
.51 
28 
2529 
PteilnponrUj W. T. T . T .. T . 
1855 
Dr. B. Surkley. 
In ale ' 
.43 
.75 
1.00 3.23 
1.20 
.40 
.61 
2533 
Tomales Bay, Cal. 
1855 
G. Samuels. 
...do .... 
.40 
.80 
1.05 2.88 
1.08 
.35 
.56 
1 Length of body before skinning, 3.60; of tail, 1.13. 
