SCIURIDZ—SPERMOPHILUS. 821 
arranged all the other American Spermophili. 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 steod 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, high, pointed (larger and more pointed than in some species of Sciurus); tail long, 
full, and 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. annulatus ?. 
Subgenus CoLopotis Brandt (emend.). 
Ears small, sometimes marginiform ; tail short, flattened, with the hairs one-third to one-half the 
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. richardsoni, S. empetra, 
S. mollis, S. spilosoma, S. obsoletus. 
Subgenus Ictrpomys* nob. 
Ears generally sinall, 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 and narrow; 
first upper premolar usually rather small, and the dentition not heavy. Species, S. tereticaudus, S. mexi- 
canus, S. tridecemlineatus, S. franklini. 
In Otospermophilus, 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 
*EryM.—ixric = weasel, and ve = mouse; in allusion to the slender Musteline form of most of 
the species. 
