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114 



MONOGRArnS OP NORTH AMERICAN RODENTrA. 



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those of llic subgenus of wliicli it is tlio type and only representative, and 

 probably most of tlicm have already been mentioned in our account of Ory- 

 zomys. The aniinal 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 Mas decumanus that one might 

 almost be excused for making the mistake. The tail, as usual, varies still 

 more than the body in lengtii. The body and tail average, perhaps, about 

 equal to each otiicr 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 

 10.} inches; figures far above any reached by any other North American 

 Hesperomys (the largest H. californicus falls short of 9 J in the same measure- 

 ment). The general range of variation is much the same as in other Hespero- 

 mys. This, with the absolute size and relative proportion of parts, is so fully 

 illustrated in the table below that 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 

 siiarply 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 H. 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 involvfes 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 arc whitish, of varying pitrity, but rarely 



