OF THE UNITED STATES 405 



sive than it is in our little flying squirrels, for it is not only a 

 lateral extension, but interdigital and interfemoral (as in bats) 

 besides. They are nocturnal, too, and feed upon insects and the 

 leaves of certain trees. It is capable of taking immense flights, 

 has but a single young one at a time, possesses pectoral mammae, 

 as in bats, and has some very remarkable habits. So, from what 

 I have endeavored to present above, it will be seen that our mod- 

 est little flying squirrels apart from the bats are not the only 

 mammals that are capable of flight of a certain kind, for they are 

 indeed the least conspicuous, perhaps, among the forms thus en- 

 dowed. 



Passing once more to a brief consideration of the Kodentia as 

 a whole, it is to be observed that the best authorities among 

 modern classifiers of mammals, divide the order into two sub- 

 orders, viz., the Simplicidentata, and the Duplicidentata. Both of 

 these suborders are represented in the fauna of the United 

 States; the first containing ten families, and the latter but two; 

 the Sciuridw being the first family of the Simplicidentata. This 

 family contains, in addition to the genus of flying squirrels 

 (Sciuropterus), just considered, the woodchucks or marmots 

 (Arctomys) ; the chipmunks (Tamias) ; the spermophiles (Sper- 

 mophilus) ; and the typical arboreal squirrels (Sciurus). 



Of the Chipmunks or Ground Squirrels there are quite a num- 

 ber of species and subspecies in the United States, and these are 

 constantly being added to by new discoveries. As a group, they 

 are well-represented by our common eastern Chipmunk, familiar 

 to every one who knows anything of our smaller mammals of the 

 Atlantic States. Some of the other forms resemble it quite 

 closely, while others depart more or less from it in the matters 

 of size and coloration; some are distributed over a considerable 

 geographical area, others being more or less restricted to their 

 ranges, thus offering descriptive zoologists abundant oppor- 

 tunity to describe the fine intergrading forms as new subspecies, 

 an opportunity that has been fully availed of, by a few ambitious 

 mammalogists more anxious to add to a personal reputation, 

 than to be of any special use or aid to the science which they 

 pretend to advance. 



While collecting in New Mexico during the 80's I obtained 

 numerous specimens of the Gila chipmunk, a subspecies wherein 

 the lateral longitudinal dorsal stripes are almost entirely ab- 

 sent (Fig. 108), though a medium one is quite distinct. 



