562 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
erally. Some of them are colorless, like the hairs upon the face; and, indeed, 
there is upon the back of the fore arm a special tuft of long colorless bristles, 
quite like the shorter whiskers. The long scattered hairs of the upper parts 
are black, giving a darker tone to the reddish-brown or chestnut of these parts ; 
on the under parts, the cast is more grayish. ‘The basal portion of the pelage 
is dark plumbeous above, paler or grayish below. I have not sufficient mate- 
rial to indicate the range of individual color-variation. Some specimens are 
said to be quite blackish. None of those examined show a pure white throat- 
patch, spoken of by some writers; but it is indicated in’ some cases by a few 
white hairs. The hands, feet, and ears appear whitish, at least in contrast 
with the general dark body colors; and the short pelage of the lips, anus, 
and preeputial sheath is usually more or less whitened. The claws are nearly 
colorless; the incisors are yellow. ; 
The anus is situate a considerable distance from the root of the tail. In 
the male, owing to the size of the os penis, the sheath of the penis forms a 
large conical projection immediately in front of the anus, and is directed more 
or less backward ; it is hairy, with a long, slender, terminal pencil. The penis 
may be readily protruded in alcoholic specimens. There is no appearance of 
a glans. The bone extends to the end of the member; it is elsewhere 
described. I have, seen no female specimens. There are said by Richardson 
to be six mamme, the position of which is indicated by brown circular marks, 
the anterior pair being situated between the fore legs. 
B.—DESCRIPTION OF THE TEETH. 
The incisors offer nothing specially noteworthy. They are very stout 
for the size of the animal, their anterior faces perfectly smooth, convex in 
both directions, the sides much bevelled. The under, as usual, protrude 
farther than the upper, and also incline farther forward as they ascend, the 
upper being perpendicular. The upper are separated from each other at base 
by a considerable alveolar interval, but incline toward each other, their points 
being in contact; the under are more nearly parallel. 
The molar series occupies a more posterior position than may be 
usual in Rodents, the anterior true molar being opposite the middle of: 
the skull. The whole series is about one-fourth as long as the skull. The 
inner alveolar border is parallel with its fellow; the outer is slightly 
divergent, owing to increase in size of the teeth from behind forward,—from 
