764 MONOGRAPHS OF NORTH AMERICAN RODENTIA, 
This species, in size, proportions, and in the color of the dorsal surface, 
is almost inseparable from var. rufoniger of S. estuans; it is, however, readily 
distinguishable from that species by the generally almost wholly gray color of 
the ventral surface, over which the hairs are conspicuously dusky at the base, 
and by the white instead of red edging of the tail. It furthermore has two 
premolars, the first quite large for a Sccwrus, while in the large number of 
specimens of both varieties of S. estwans I have examined I have found uni- 
formly only one. It is so wholly distinct from all the other Scéwri as to require 
no detailed comparison with any of them. 
The seven specimens of this species before me vary in respect to color- 
ation as follows: —One (No. 7849, Orizaba, Mexico) is pure gray below through- 
out, the hairs being tipped with white aud dusky at base; above, olivaceous- 
dusky, minutely punctulated with yellowish-rufous; middle of the back 
blackish; ear-patch whitish. No. 7206, also from Orizaba, is similar, except 
that the sides are rather more strongly varied with yellowish-rufous, and the 
pectoral region is distinctly washed with fulvous. No, 8491, from near Cor- 
dova, is almost exactly like the last, being perhaps rather more fulvous below 
and a little redder on the flanks. Another (of which the label is lost) is still 
more rufous above and more fulvous below. No. 8490 (Cordova) is like the 
last, with, however, distinctly white ear-patches. No. 3922 (Mexico) is more 
rufous above, and is washed strongly with reddish-fulvous below. No. 38261 
(Mexico) is bright orange below, but above is wholly like the gray-bellied 
specimens from Orizaba. No. 8620, from Central Guatemala, is fulvous- 
washed below, but is strongly ferrugineous above, with reddish-yellow ear- 
patches, the prevailing color dorsally being ferrugineous, slightly varied with 
black. In this specimen, the hairs of the dorsal surface are double-ringed 
with fulvyous, plumbeous at base, then a narrow ring of fulvous, followed by 
another of black, and tipped with rusty. In all the other specimens, the 
hairs are wholly blackish, except the tip, which is yellowish, varying more or 
less in different specimens to rufous. 
Or the eight specimens of this species before me, seven are from 
Southern Mexico and the other from Guatemala. Dr. Gray refers to his 
M.-tephrogaster specimens from “ Mexico (Sallé), Guatemala (Salvin), Hon- 
duras (Dyson), and. Bogota (H. E. Strickland)”; I also refer to the same 
species his MM. teniurus from Guatemala, his Jf. middellinensis from Antio- 
guia, New Granada, and less confidently his If fraseri from Eeuador. The 
first three of these names I think are unquestionably referable to this species. 
