RODENTIA—ARVICOLINAE—ARVICOLA BREWERI. 525 
very much better than to 4. riparia, in which not one of these characters exists, the differences 
being in color, length of tail, and position of teats. Thus, the tail of riparia is fully twice 
the proportional length indicated, the color is much darker, and there are two pairs of pec- 
toral teats, in addition to the inguinal ones. Even if A. pinetorum be out of the question, there 
is another species in Pennsylvania, which I do not now describe, of redder color and shorter 
tail than riparia, and of nearly the same size. I feel, therefore, fully justified, in view of the 
uncertainties of the case, in preserving the name of riparia. 
ARVICOLA BREWERI, Baird. 
Gray Mouse. 
Sp. Cu.—Size large. Feet very broad and stout ; soles with six tubercles. Furcoarse. Ears small. Above, pale grayish 
yellow brown ; beneath, with the under surface of the tail and the upper surfaces of the feet strongly hoary or ashy white, 
with a tinge of yellow. 
This species is among the largest of those found in the eastern United States, in fact con- 
siderably exceeding any I have ever seen from within this limit. The head is very broad, the 
upper outline much curved; the ear only moderately large, orbicular, the antitragus much 
developed, the auricle well covered with hairs on both sides. 
The feet are broad and stout, the hind claws longest; the thumb is armed with a short but 
pointed and curved claw, rather larger, apparently, than in some other species. There are six 
tubereles on the soles, the posterior inner large, the posterior outer quite small and incon- 
spicuous. 
The prevailing color of this species above is a yellowish gray, or grayish yellow brown ; 
quite different in its pallid tint from any other American species I know of. The entire under 
parts are of quite a pure yellowish white, this color extending nearly half way up the sides. 
The under part of the tail is similar, imparting to it a strongly bicolor appearance ; the upper 
surfaces of the feet are also white, with perhaps a faint tinge of plumbeous. 
The skull is strictly that of section A, but presents some peculiarities in the narrow dimensions 
behind the zygomatic arch, and other features. The most prominent among these is in the 
shape of the interparietal bone, which is longer than usual, and laterally sends out on either 
side a long point, the axes of which are in the same straight line, and but little behind the 
middle of the bone. In most of the other species this bone is truncate laterally, without the 
long point. 
This species differs decidedly from any other I know in the pallid tints above and the white of 
the under part, where the hairs are white for nearly half their length. The fur is very coarse, 
and not compact; much like that of Sigmodon. 
The only specimens of this species I have ever seen were collected by Dr. Brewer, on the island 
of Muskeeget, on the eastern coast of Massachusetts, where they are said to be abundant. 
