MURIDA—ARVICOLINE—ARVICOLA XANTHOGNATHUS. 199 
The under parts are uniformly strong hoary-ash, owing to whitish tips of the 
very deep plumbeous fur. The hoariness varies much, sometimes being 
scarcely evident, and at other times being soiled with a brownish or clay- 
colored wash. The very edges of the lips are apt to be whitish; the 
whiskers are whitish and dark; the incisors yellow, the upper generally 
deepest-tinted, the under frequently nearly white. 7 
We will finish consideration of color before taking up the matter of the 
measurements. Our remarks are based upon an examination of several 
hundred specimens. 
The range of individual variation appears to us comparatively slight. 
This is probably due to the rather homogeneous character of the localities 
whence our specimens came. Some are a little darker, or a little lighter, 
browner, grayer, more grizzly, &c., than others. But we see nothing that 
calls for special remark in this connection. One (No. 6594) is an incomplete 
albino, having a broad zone of pure white around the head and neck, thence 
extending along the breast and belly, and flesh-colored ears. 
Certain seasonal conditions of pelage are strongly marked. In the 
spring, just after the animal has shed its old winter coat, it appears in a fur 
very noticeably shorter, finer, smoother, and glossier than it is at other 
seasons; and the color is so different as to readily suggest specific distinction 
to one ignorant of the facts in the case. At a little distance, the animal 
looks almost black, so dark is the shade. The brown of the upper parts is 
almost a blackish mahogany-color, with little or no admixture of fulvous, 
tawny, or yellowish-brown, while the plumbeous below has corresponding 
intensity and is but slightly hoary. The tail is nearly unicolor. As the season 
advances, the depth of color insensibly lessens; the grayest and grizzli- 
est animals are those that wear the oldest pelage in the fall and winter. 
But we do not notice, in these or other changes, any marked difference in 
the cheeks, the distinctive brand of the species usually remaining much 
the same. 
On the other hand, individual variations in stze are as great as we have 
succeeded in demonstrating for r/parius with our immense array of specimens 
from all localities; and this is the more remarkable, seeing that canthognathus 
is so restricted in its geographical distribution that climatological influences 
are hardly brought to bear upon it. We invite particular attention to the 
subjoined table that demonstrates the variability we continually insist upon 
