758 MONOGRAPHS OF NORTH 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 the 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. estuans. Length of body about 8.75; 
of tail-vertebree about 7.00 to 7.75; of tail to end of hairs 9.00 to 9.75. 
Scarcely different in coloration from var.@stuans, 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. @stwans are of just the same tint above 
as var. riifoniger, 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 ; 
