RODENTIA : MURID^:. 97 



1. Dipodinae are characterized by unequal, generally 

 rooted molars, and greatly elongated hind legs. 



The Genus Dipus Jerboas is characterized by a 

 large head, long, densely hairy, and tufted tail, hind legs 

 which are exceedingly long in comparison with the for- 

 ward ones, and by the metatarsus of the three middle toes 

 which is formed of a single bone, and by the three upper 

 molars on each side. The Jerboas move about on their 

 hind feet, making great leaps. The ancients called them 

 Biped Rats. They belong to Africa and Asia. 



The Genus Jaculus has the hind legs and tail very 

 long, the latter thinly haired, the hind feet five-toed, and 

 the upper molars four on each side. 



The Jumping Mouse, or American Jerboa, J. Imdsonius, 

 Baird, of Labrador and southward and westward to the 

 Pacific, is about three inches long to the tail, which is 

 four to six inches ; the col- Fig 82 



or above light yellowish- 

 brown lined finely with 

 black, beneath white, and 

 the sides yellowish-rusty, 

 sharply defined against 

 the colors of the back and 

 belly. When startled it Jumping Mouse, 7. 

 progresses by very long and rapid leaps, and there is 

 probably no other mammal of its size that can make its 

 way over the ground with so great rapidity, or so quickly 

 escape from its pursuers. 



The Genus Gcrbillus, Gerbils, of the warm parts 

 of the Old World, belongs near this group, if not in it. 



2. Murinae have compressed incisors, molars ^ or ^^ 

 and rooted, the largest anterior, and the smallest poste- 

 rior. They comprise Mures and Sigmodontes. 



a. Mures, or the Old- World Rats, are characterized by 

 very large and broad molars, and those in the upper jaw 

 have three tubercles in each transverse series. 



