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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, Sciwromorpha, 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. 
Famiry SCIURID. 
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 aglance. 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 Sciwride. 
The Scituromorpha have perfect clavicles, nearly free forearm 
bones, small incisive foramina, large and distinct malar. The 
nasal pad is small and the upper lip cleft. Inthe Sciuride post- 
orbital processes are present and the molars are provided with 
tuberculed crowns. Dental formula: i }:4; pm. ?:?m. 3:3. 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. 
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