ZAPODlDiE— ZAPU8 HCDSON1U8— EXTERNAL CHARACTERS. 475 



In its relative length, the tail exceeds that of any other North American 

 (iiiamiiial J) Roc'ent, always greatly exceeding the head and body, and some: 

 times measuring nearly twice as much. It is cylindrical, with uniform taper 

 and very slight caliber^ coming to a fine point with a slight pencil of hairs. 

 Its hairiness is about on a par with that of Mm musculus, decumanus, &c. ; 

 that is to say, insufficient to hide the verticillate whorls of scales between 

 which the short hairs spring. 



The general pelage of this animal is coarse and hispid, with little gloss, 

 .and presenting a streaky or "staring" appearance, owing to the number of 

 bristly hairs which are mixed with the softer under fur. The color varies a 

 good deal in diiferent specimens, though one pattern is pretty constantly pre- 

 served. About one-third of the colored part of the fur — that is to say, a 

 dorsal strip about as wide as the lateral strip on either side — is brownish- 

 yellow, heavily shaded with brownish-black. The sides, with the outer 

 surface of the limbs, are of this sai le sandy-yellowish, but so slightly lined 

 with the blackish that the purity of the light color is scarcely interfered with. 

 The under parts are snow-white, with a pretty sharp line of demarkation 

 from the colored areas. The backs of the hands ami feet are whitish. The 

 tail is rather indistinctly bicolor, to correspond with the body-areas, — -aark 

 brown above, whitish below. The ears have a light-colored rim. The 

 whiskers art mostly black. The basal part of the fur, in the colored areas, 

 is gray or plumbeous, excepting just along the line of junction of the tawny 

 of the sides with the white of the belly, where the hairs are white to the 

 roots, like those of the belly. To this absence of dark bases of the hairs is 

 due the appearance of a fulvous stripe along the sides, sometimes quite 

 strongly marked, much as in species of Perognathus or Cricetodipuf . In these 

 coses, there are thus four styles of coloration from back to beliy : the dark 

 dorsal area, mixed blackish and sandy, with plumbeous roots ; sandy, with 

 little or no blackish, but still with gray roots, sandy, with white roots; and, 

 finally, pure white. The variations (o which the species is subject lie in the 

 brightness or dullness of the tawny, and its lining with a varying amount of 

 blackish ; the degree of distinctness of the dorsal area from that of the sides, 

 and of this from the white of the belly ; and in the sharpness or indistinct- 

 ness; of the tawny lateral stripe along which the hairs are white at the roots. 

 The line of the belly-white is pretty constantly sharp, as in Hesperomys; but 

 there is often a gradual shading from the dark dorsal area to the tawny 



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