154 BULLETIN NO. VII. 



ited by the rodent tribes. From the flying squirrels of West 

 Africa, as large as a cat, to our own diminutive Sciuropterus 

 volucella, from the blind mole of the Cape to our pouched 

 gopher, from the springing mice of the Sahara to our shy 

 Zapus hudsonius, there is variety enough to interest the most 

 fastidious. 



Rodents are divided into two suborders upon the structure of 

 the teeth. The first, SIMPLICIDENTATI, includes the three 

 series, Sciuromorpha, Myomorpha, and Histricomorpha, inclu- 

 ding respectively animals with resemblance and affinity to the 

 squirrel, mouse and porcupine. 



The second suborder, DUPLICIDENTATI, includes the hares 

 and picas. 



FAMILY SCIURIDCE. 



SQUIRRELS. 



This family includes a variety of animals varying greatly in 

 structure, but unmistakably related. Even the flying squirrels 

 do not differ so essentialy from the prairie dog or woodchuck 

 that the affinity can not easily be seen at a glance. Active and 

 rather social and pleasing animals, for the most part, but num- 

 bering some petty raiders among them, we shall not be likely 

 to neglect the Sciuridce. 



The Sciuromorpha have perfect clavicles, nearly free forearm 

 bones, small incisive foramina, large and distinct malar. The 

 nasal pad is small and the upper lip cleft. In the Sciuridce post- 

 orbital processes are present and the molars are provided with 

 tuberculed crowns. Dental formula : i \ :-}-; pm. f :|- m. f :f. The 

 number of premolars often varies in the same genus, there 

 being in many cases but one on a side above. The tail is hairy 

 and generally bushy, the feet well clawed. Habits fossorial, 

 scansorial, or partly volant. Considerable variation obtains in 

 the configuration and minor details of the skull and skeleton, 

 as will be seen. Eight genera are recognized, six of which 

 occur in our district. 



The squirrels constitute the genus Sciurus, standing at the 

 head, while the rear is brought up by the more primitive type 

 represented by Arctomys, the woodchuck. The two genera not 

 found in America are Pteromys and Xerus, found in India and 

 Africa respectively, the latter being in some respects like the 

 porcupine. 



