658 COLLEGE ZOOLOGY 



P. hispida, and the harp seal, P. grcenlandica, live in the Arctic 

 seas; Pallas' seal, P. largha, is the seal of the North Pacific. 



Order Rodentia (GLIRES). GNAWING MAMMALS. The 

 rodents are characterized by their long, chisel-shaped incisors 

 (Fig. 511, 14, 16), which are adapted for gnawing, and the ab- 

 sence of canines, leaving a gap between the incisors (14) and pre- 

 molars (15). They are all small or of moderate size, and num- 

 ber over fourteen hundred species, constituting the largest order 

 of mammals. South America is richest in the number of species. 

 The best-known North American families are the rabbits and 

 hares (LEPORID^:), the squirrels (SCIURID^E), the beavers (CAS- 

 TORID.E), the pocket-gophers (GEOMYID^E), the rats, mice, etc. 

 (MURID.E), and the porcupines (CCENDID^E). 



The LEPORID.E, or rabbits and hares, differ from most other 

 rodents in the possession of a pair of small incisors just behind 

 the pair of large incisors in the upper jaw. The more common 

 American species are the cottontail, or gray rabbit, Sylvilagus 

 floridanus mallurus, the varying hare, or snow-shoe rabbit, 

 S. americanus, and the jack-rabbit, S. campestris. 



The family SCIURID.E includes the woodchucks, prairie-dogs, 

 tree-squirrels, chipmunks, ground-squirrels, and flying squirrels. 

 There are about one hundred and seventy species and geographic 

 races in North America. The common tree-squirrels (genus 

 Sciurus) are the gray, fox, and red squirrels; these are all excel- 

 lent climbers, and possess large, bushy tails. They become 

 quite tame if unmolested, and with the probable exception of 

 the red squirrel or chickaree, should be protected. 



The chipmunks or rock squirrels (genera Eutamias and Tam- 

 ias) are small animals living usually on the ground among rocks 

 (Fig. 522). The ground-squirrels (genera Citellus, Callospermo- 

 philus, and Ammospermophilus) are sometimes called gophers. 

 They are inhabitants of open country and dig burrows in the 

 ground. Their food consists of grain which they carry into 

 their burrows in cheek-pouches. The prairie-" dogs " (genus 

 Cynomys) are burrowing rodents that live on our western plains 



