780 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
in Sciurus; pelage generally full and soft; dorsal surface generally with two 
(sometimes four) longitudinal whitish stripes, bordered on each side with a 
stripe of black, and with (except in one species) a central dorsal stripe of black. 
As already stated (anted, p. 639), Tamias bears a strong resemblance to 
some of the smaller species of Spermophilus, the two groups being in fact 
not sharply separable. The more important differences are the following :— 
In Tamias, there is sometimes but a single upper premolar, and when two 
are present the first is very minute, scarcely larger than in Scewrus hudsonius ; 
in Spermophilus, two are always present, and the first is functionally devel- 
oped, being from one-fourth to one-half the size of the second. In Tamias, 
the whole dentition is weaker and the teeth relatively smaller; the ante- 
orbital foramen is oval (sometimes quite narrow), and the outer and lower 
border is not generally developed into a projecting bony rim, culminating in 
a tubercle, asin Spermophilus. The notch in the posterior border of the zygo- 
matic maxillary process is situated more anteriorly than in Spermophitus. 
The skull is much more delicate and papery than in Spermophili of corre- 
sponding size, and shows no traces of the muscular ridges often seen in old 
skulls in the genus Spermophilus. The tail is usually also more flattened, and 
the general form of the animal is more Sciurine. 
Tamias differs from Scivrus in the form and position of the anteorbital 
foramen; in the greater obliquity of the plane of the zygoma and its more 
gentle downward deflection; in the more regularly oval, flattened, and 
depressed form of the skull, and especially in the skull being‘more narrowed 
anteriorly and in the nasal portion being more produced; in the molar series 
being divergent anteriorly instead of parallel; in the form of the lower jaw, 
which is slenderer, with the coronoid process longer, narrower, and more curved; 
in the possession of capacious cheek-pouches, and shorter and narrower tail. 
As above diagnosed, Tamivs includes two species referred by Professor 
Baird to Spermophilus, and hence members of the two commonly recognized 
“subfamilies” of the Scéwride! These species are Spermophilus harrisi and 
Spermophilus lateralis. The latter makes a considerably nearer approach to 
the Spermophiles than does the former, but in all essential features they both 
much more nearly agree with the species usually referred to Tamias than 
with any of the Spermophiles. In respect to the skull, 7. harrist scarcely 
differs in any feature from T. astaticus (=quadrivittatus et pallasi auct.) var. 
townsendi, and could scarcely with certainty be distinguished from it except 
that the skull of 7. harrisi is rather the larger. The first premolar is as 
