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 OTOSPERMOPHILVS, 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 the skull, and the dentition, strongly 

 Sciurine. 



Sub-genus COLOBOTIS, 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. 



