114 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
those of the subgenus of which it is the type and only representative, and 
probably most of them have already been mentioned in our account of Ory- 
zomys. The animal varies a great deal in size, from the dimensions of a 
third-grown house-rat up to the size of a small individual of that species ; 
and these larger ones really look so much like Mus decumanus that one might 
almost be excused fur making the mistake. The tail, as usual, varies still 
more than the body in length. The body and tail average, perhaps, about 
equal to each other in length; the former ranges usually from about four to 
five and a half inches in length. In the largest specimen before me, No. 
3327, from Neosho Falls, Kans., the total length of trunk and tail together is 
104 inches; figures far above any reached by any other North American 
Hesperomys (the largest H. californicus falls short of 9$ in the same measure- 
ment). The general range of variation is much the same as in other Hespcro- 
mys. This, with the absolute size and relative proportion of parts, is so fully 
illustrated in the table below tbat further notice here is unnecessary. 
The pelage of this animal is rather coarse, if not harsh, but it is glossy 
from the great proportion of long, glossy, soft bristles that it has. Perhaps 
the most interesting point in this connection is the unequal hairiness of the 
upper and under surfaces of the tail. On top, this member is so scantily hir- 
sute that the pavement of granular reticulations is distinctly visible; below, 
the plates are generally hidden by longer and more numerous hairs. The 
difference is most evident in those tails that are distinctly bicolor. There is 
a great range of variation in this latter regard; some tails being almost as 
sharply bicolor as in H. leucopus, while others are merely a little paler below 
than above. In this case, as in others throughout the genus, we have often 
thought that the difference is not so much an individual matter as one depend- 
ent upon season, age, and state of health; and that the same individual may 
change in this respect. Like HZ. aureolus (nuttalli), this animal does not show 
the sharp dividing line along the sides between the colors of back and belly ; 
the two generally blend insensibly. The darker color always reaches down 
the limbs to the ankle and wrist, and involves the extremity of the snout, 
although the lips and cheeks are like the belly. The color is a mixture of 
yellowish-brown, grayish-brown, and black, producing the grizzly rat-color 
impossible to name. The mixture is very intimate; only the lighter shades 
prevail over the sides and rump, and the darker along the dorsal area, some- 
times producing a pretty distinct stripe, but oftener shading insensibly into 
the general hue. The under parts are whitish, of varying purity, but rarely 
