780 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



in Sciurus; pelage generally full and sofl ; dorsal surface generally with two 

 (sometimes four) longitudinal whitish stripes, bordered on each side with a 

 stripe of black, and with (excepl 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 

 arc present the first is very minute, scarcely larger than in Sciurus 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, 

 (lie, 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, as in Spermophilus. The notch in the posterior border of the zygo- 

 matic maxillary process is situated more anteriorly than in Spermophilus. 

 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 Sciurus 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, Tami'is includes two species referred by Professor 

 Baird to Spermophilus, and hence members of the two commonly recognized 

 "subfamilies" of the Sciuridw,! These species arc Spermophilus harrisi and 

 Spermophilus lateralis. The latter makes a considerably nearer approach to 

 the Spermophiles than docs 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, T. harrisi scarcely 

 differs in any feature from T. asiaticus (—quadrivittatus et pallasi auct.) var. 

 townser/di, and could scarcely with certainty be distinguished from it except 

 that the skull of T. harrisi is rather the larger. The first premolar is as 



