5)3G MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



fuscous to a greater or less extent and intensity. Some specimens, with the 

 least dusky, are very light colored — a pale yellowish-cinnamon; others 

 approach mouse-color, but even in the darkest specimens the decided fulvous 

 shade appears at least upon the sides. All this colored portion is plumbeous 

 beneath, excepting a little space along the middle of the sides, where bat-ally 

 white hairs have the tawny tips. All the under surface of the animal is snow- 

 white to the roots of the hairs. The line of white begins on the side of the 

 muzzle and runs along the side of the head, including the pouch; the entire 

 fore limb is white ; the stripe rises a little on the side of the belly, and thence 

 runs along the middle of the outside of the hind limb from the knee to the 

 heel, sending a sharp white stripe from the knee across the haunches to the 

 root of the tail. The hind foot is white, with a dusky stripe along the sole. 

 The whiskers are partly black, partly colorless; their conjoined bases make a 

 conspicous black spot on each side of the muzzle. There is some whitish- 

 ness in most cases — sometimes altogether wanting — about the eye, and a white 

 patch just back of the ear. The front of the ear is sometimes light. The 

 tail is dusky-slaty, or sooty-brown, or even blackish, with a broad, firm, white 

 stripe on each side from base to near the tip. At the extreme base, the white 

 usually encircles the tail ; at the other end, the color of the tuft is altogether 

 indeterminate; sometimes the white lateral stripes give out before reaching 

 the end, leaving the tip entirely dark ; sometimes the white extends to the 

 very end of the brush, cutting off the dark altogether; and, moreover, the 

 white may encroach upon the under side, cutting off the dark from more than 

 half the tail ; oftener, the brush is mixed dusky and white. Thus the tail 

 may end either white or dark, or a mixture of both. It is as variable in this 

 respect as the tail of a skunk. The eyes are lustrous black ; the nose-pad 

 and palms flesh-colored ; the claws pale. 



In old museum specimens, long exposed to the light, the above descrip- 

 tion may not be verifiable as regards any of the darker markings and shades 

 mentioned; for all the colored portions of the fur finally fade to a dull, pale 

 brownish-yellow, or even dingy yellowish-white. Under such circumstances, 

 even the rich purplish-chestnut of a mink, for example, ends in dingy whitish. 

 Discussion of (he species of Dipodomys. — Having thus fully exposed the 

 characters of the animals of this genus, it remains to consider the mode in 

 which, and extent to which, the genus has become differentiated into recog- 

 nizable forms, if there be more than one. Various species have been pro- 



