740 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
blance to that of northern specimens of S. carolinensis, particularly to those 
with a large brownish dorsal area. A careful comparison, however, shows 
the absence of the fulvous suffusion below the surface of the pelage seen in 
that species, and the absence of any tawny lateral line. The tail also is much 
longer, and more than one-third fuller and broader, with quite different col- 
oration, being distinctly tricolored below, with the three colors strongly con- 
trasted and sharply defined,—centrally a broad band of bright tawny, nearly 
two inches wide, with indications of two narrow bars of black within it on 
each side of the vertebrae; outside of this is a band of deep black, one-half 
to one inch wide, with, beyond this, a broad clear white margin. The hairs 
are, many of them, fully three inches in length, so that the tail, measured 
across the middle from point to point of the outstretched hairs, has a breadth 
of six inches. The Mazatlan specimens have the tail rather less full, and 
the bright tawny central area is simply pale fulvous,—a difference of no 
great importance, in view of the differences in this respect presented by 
specimens of S. carolinensis from even a single locality. 
The ears are low, broad, and round, not half as large as in S. aberti, and 
less pointed, shorter, and broader than in S. fossor. This species is further 
distinguished from S. fossor by its shorter tail, more brownish-gray color of 
the upper surface, and by the presence of a yellowish-brown dorsal area, 
covering nearly all of the back. 8. colli@i is distinguishable from S. aberti 
not only through the great difference in the size and form of the ears and 
the absence of ear-tufts, but by lacking the black lateral line, and by the 
dorsal brownish area being pale yellowish-brown instead of reddish-brown or 
chestnut. The S. deporinus of Audubon and Bachman, from “California”, 
greatly resembles S. colliai in color, size, and form, and is, I have little doubt 
referable to this species. Its supposed locality is doubtless wrong, being 
not the present State of California, but from some point farther southward. 
I have seen, however, a specimen of S. fossor, in an evidently abnormal con- 
dition of pelage, corresponding quite well with the description of S. Zeporinus. 
The description of Sciwrus oculatus of Peters, in respect to size, colora- 
tion, relative length of the tail, ete., agrees with the usual phase of S. colliai. 
