SCIUUIDyE— SPEKMOPUILUS. 821 



arranged all the other American Sp'rmophili. He also recognized the highly 

 Sciurine character of the Otospermophili, which he regarded as "only distin- 

 guishable externally by the cheek-pouches" from the true Squirrels. Colo- 

 botis, however, as thus left, embraced very diverse types. 



While, as already stated, it is impossible to subdivide the American 

 Spermophili into sharply definable groups, they admit of arrangement in 

 three sections, of which the extreme phases of differentiation are as wide 

 asunder as are most allied modern genera, but which still thoroughly inoscu- 

 late through variously intermediate specific forms. If their most differentiated 

 specific representatives stood alone, even the generic distinctness of these 

 groups would be unquestioned. As already intimated, one of these deviating 

 lines is in the direction of Cynomys, another in the direction of Tamias, and 

 the third tends strongly toward Sciurus. Provisionally recognizing these 

 sections as subgenera, they may be characterized as follows: — 



Subgenus Otospermophilus Brandt (emend.). 



Ears large, nigh, pointed (larger and more pointed than in some species of Sciurus) ; tail long, 

 full, ami broad, with the hairs two-thirds to three-fourths the length of the head and body; general 

 form of the skull, and the dentition, strongly Sciurine. Species, S. grammurus, S. annulatust. 



Subgenus Colobotis Brandt (emend.). 



Ears small, sometimes marginiform ; tail short, flattened, with the hairs one-third to one-half Ihe 

 length of the body ; skull short and broad, the zygomatic arches broad, generally greatly widened pos- 

 teriorly ; dentition heavy, and the first upper premolar generally large. Species, .S'. richardsani, S. empelra, 

 <S'.' mollis, S. spilosoma, S. obsohtus. 



Subgenus Ictidomys* nob. 



Ears generally small, sometimes rudimentary; tail long, cylindrical, or narrow and flattened, or 

 quite broad, with the hairs one-half to three-fourths the length of the body ; skull very long aud narrow ; 

 first upper premolar usually rather small, and the dentition not heavy. Species, S. tereticaudus, S. mexi- 

 canus, S. tridccemlineatus, S. franklin i. 



In Otospermopiiilus, the first upper premolar is scarcely larger than in 

 some species of Sciurus; the skull is similarly arched and expanded; the 

 anteorbital foramina are narrower, and their outer walls are thinner than in 

 the other Spermophiles. The cranial differences relate, mainly to the greater 

 obliquity of the malar bone and the greater lateral expansion of the zygo- 

 matic processes of the maxillaries. <S. empetra (=parryi of authors) is but a 

 little way removed from the group, and forms an easy passage to Colobotis. 



In Colobotis, the skull is shorter and broader, generally much arched, 

 the zygomatic arches more spreading, and the dentition heavier; in all these 

 characters, as well as in the short flat tail and the thick-set form, the group 



* Etym. — iktic = weasel, aud /ivc — mouse; in allusion to the slender Musteline form of most of 

 the species. 



