758 MONOGRAPHS OF NOBTII AMERICAN RODENTIA. 



form in coloration, varying mainly in respect to the tint of the lower surface, 

 which ranges from yellowish-white to reddish-yellow. The upper surface, 

 though presenting a small amount of variation in comparison to that shown 

 by (he Central American and Mexican species, varies considerably in respect 

 to the general tone of the color. The hairs are generally plumbeous or dusky 

 at base, ringed first with yellowish-brown and then with black, with yellowish 

 tips. The hairs are thus twice ringed with black and yellowish. The gen- 

 eral color varies from mixed yellowish-gray and black to mixed reddish-brown 

 and black, with sometimes the middle of the back distinctly darker than 



the sides. 



Var. RUFONIGER. 



Varietal chars. — Larger than var. ostiums. Length of body about 8.75 ; 

 of tail-vertebrae ahout 7.00 to 7.75; of tail to end of hairs 9.00 to 9.75. 

 Scarcely different in coloration from \ar.astuans, except that the dorsal surface 

 is rather darker and redder and the lower parts rather lighter ; the tail is also 

 washed with yellowish-red instead of very pale yellow, while the black rings 

 are broader and darker. 



In respect to the general coloration of the body, these two forms are 

 sometimes quite indistinguishable, but the coloration of the tail is generally 

 strikingly different; the size of the northern form seems also to be uniformly 

 larger. Occasionally, specimens of var. cestuans are of just the same tint above 

 as var. rufoniger, but generally var. rufoniger is redder and darker, the middle 

 of the back being frequently quite blackish, the hairs being ringed with red- 

 dish-yellow and black instead of pale or grayish-yellow and black, with the 

 subterminal black ring broader. 



Among the twenty-five or more specimens of var. rufoniger in the col- 

 lection (nearly all from Costa Rica), the range of color-variation is very lim- 

 ited, the dorsal surface varying only in respect to the amount and intensity 

 of the rufous, and in respect to whether the middle of the dorsal region is 

 concolor with the rest of the dorsal surface, or more or less darker. The 

 lower surface varies from dull pale reddish-fulvous to deep bright orange. 

 The tail varies only in respect to the tint of the reddish edging, which is 

 sometimes yellowish-red, but generally reddish-orange, and not unfrequently 

 dark reddish-brown. The very small inconspicuous ear-patch varies from 

 white or yellowish-white to reddish-fulvous. The outside of the limbs and 

 the upper surface of the feet are generally colored like the dorsal surface; 



