SCICKID.33— SYNOPSIS OF GENERA. G41 



III. Skull short, broad, and rounded ; postorbital processes well developed, slender, directed downward 



and backward ; zygomatic arches usually slender, the malar expanded in a nearly vertical plane, 

 sometimes turned slightly outward dorsally ; anteorbital foramen a narrow slit, anterior to the 

 zygomatic process of the maxillary ; upper premolars either two or one < two as a rule) ; when 

 two are present, the first isahvays small and sometimes deciduous; ears moderate, well clothed, 

 and sometimes conspicuously tufted; no cheek-pouches; nail of pollex rudimentary; pelage 

 generally soft, but occasionally coarse and more or less rigid ; tail broad, with the hairs mostly- 

 directed laterally Sciurus. 



IV. Skull, in general form, intermediate between that of Sciurus and Tamias ; postorbital processes 



smaller, and the nasal bones narrower (at least than in Sciurus); no cheek-pouches; ears very 

 small or rudimentary ; tail shoit, but slightly flattened ; pelage harsh, consisting of flattened, 



grooved spines and coarse bristly hairs, with little under fur Xerus. 



V Skull narrowed anteriorly ; postorbital processes very slender, directed downward and backward ; 

 zygomatic arches more expanded and depressed anteriorly, and the plane of expansion of the 

 malar more oblique; anteorbital foramen oval, situated in the base of the zygomatic process 

 of the maxillary ; upper premolars either two or one ; when two are present, the first is gener- 

 ally minute ; large internal cheek -pouches; ears of mtdium size, well clothed, but never tufted; 

 pollex with a well developed nail; tail rather broad, but shorter and much narrower than 

 in Sciurus and Sciuroj>tcrus ; pelage soft; dorsal surface with longitudinal stripes; size rather 



small - Tamias. 



VI. Skull variable in form, being either narrow and elongate or short and broad, much as in Sci«n<« ,• 

 po8torbital processes generally triangular, strong, and directed downward; zygomatic process 

 of the maxillary depressed and expanded ; plane of the malar bone turned outward, sometimes 

 expanded nearly horizontally; zygomatic arches spreading; anteorbital foramina placed 

 more anteriorly than iu Tamias, much as in Sciurus, but rather larger and more circular, 

 with a strongly developed tubercle at the outer lower bolder; upper premolars always two 

 the first variable in size, but always larger than in the preceding genera, in some species rela- 

 tively nearly as large as in Cynomys ; grinding-teeth in some species nearly as iu Sciurus, in- 

 creasing in size in other species till nearly as strong as in Cynomys; cheek-pouches well devel- 

 oped ; body slender or thick-set ; tail long, moderate, or short ; ears large, medium, or rudiment- 

 ary, never tufted ; nail of pollex gentrally ludimeutaiy ; character of the pelage and pattern of 



coloration variable Spermophilas. 



VII. Skull strong and massive, rather short and broad; zygomatic arches widely expanded ; malar 

 rather slight, its plane oblique; muzzle narrow ; postorbital processes long, strong, and directed 

 downward; anteorbital foramina rather large, subtriangnlar, thrown outward basally, and 

 placed well forward ; upper premolars two, the first large, of the same breadth antero-posteri- 

 orly as the other grinding-teeth ; dentition very heavy, the grinding-teeth with the transverse 

 breadth twice the antero- posterior, the last molar much larger than the others, and subtriangn- 

 lar ; the molar series strongly convergent posteriorly; body heavy, thick-set ; cheek-pouehes 

 not large; tail short; ears rudimentary ; nail of pollex well developed ; pelage short and rather 



harsh Cynomyx. 



VIII. Skull with the dorsal outline nearly straight ; -frontal region flat or depressed; in other respects 

 the form is much as in Cynomys, but with heavier postorbital processes, not (or but- slightly) 

 decurved, much weaker dentition, and the molar series parallel ; interparietal and occipital 

 crests much more strongly developed than in the other genera; size large; body stout, broad, 

 depressed; cheek -pouches absent or small ; tail short, bushy ; ears small ; nail of pollex broad, 

 flat; pelage coarse, heavy Arctomys. 



In the first five genera, the skull is more or less convex above, being in 

 the first three highly arched, but generally much less so in Sper?nophilus, and 

 still less in Cynomys, while in Arctomys it is nearly straight. The postorb- 

 ital processes become much heavier in Cynomys than in the preceding genera, 

 but reach si ill greater development in Arctomys. The skull is generally des- 

 titute of ridges fur muscular attachment, but such ridges are generally trace- 

 aide in aged individuals, even in Sciurus, in which, however, they are widely 



separated, converging posteriorly. In most of the Spermophiles, they are more 

 41 M 



