164 BULLETIN NO. VII. 
both hemispheres. The spermophili are most numerous in the 
temperate and north temperate regions, and are essentially 
prairie animals. There are about equal numbers in America and 
the Asiatic-European continent. They are not found in the 
eastern portions of America; nor are they numerous in western 
Europe, so that the plains of Asia may be taken as their geo- 
graphical centre. The fossil forms, of which there are several, 
do not afford conclusive evidence upon the origin of the genus. 
Its species are very like members of several different genera: 
Sciurus (the squirrels), Tamias (the chipmunks), Cynomys (the 
prairie dogs) and Arctomys (the woodchucks). Different species 
are more like one or the other of these groups, so the group is 
rather heterogeneous and consequently difficult to diagnose. 
The form is usually slender; the tail is not so bushy as in most 
squirrels, and its hairs are usually more obviously dichotomous 
in their arrangement than in squirrels. The tail is of variable 
length but, in the majority of cases, is short and stumpy. The 
ears are never tufted as in most squirrels, but may be quite 
large; in typical forms, however, they are small and rounded. 
Like Tamias, the gophers have well developed pockets opening 
inside the mouth and operated by special muscles. There may 
or may not be a nail upon the thumb. 
Aside from these external characters there are some osteo- 
logical peculiarities. There are always two premolars i. e., 
five back teeth; the zygoma is flattened horizontally; the ante- 
orbital foramen is triangular instead of a narrow slit and is 
protected by a spur at the lower outer corner. 
The genus Tamias in habits and in structure forms the link 
between the gophers and squirrels, and the line of demarkation 
between the former is purely artificial. The genus has been 
divided into three sections or subgenera, and before passing to 
the list of species we may quote the diagnoses as revised by 
Allen, to whose paper in the Rodentia of North America the 
reader is referred for a full discussion of their position. 
‘‘Sub-genus OTOSPERMOPHILYVS, Brandt. 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 theskull, and the dentition, strongly 
Sciurine. 
Sub-genus CoLonorrs, Brandt. 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, gener- 
ally greatly widened posteriorly; dentition heavy, and the first 
upper premolar generally large. 

