30 MAMMALS. 



tibia and fibula united. Contains, probably, but a single 

 species, inhabiting the Northern U. S., related to the Old 

 World Jerboas. 



/. ZAPUS, Coues Jumping Mice. 



= Jaculvs, Wagler. 

 1. Z. hudsonius, (Zimmermann) Coues. Yellowish 

 brown. U. S., chiefly northward; variable. 



FAMILY XIV.— MURID.-E. 

 (The Mice.) 

 Incisors f ; molars usually f:|; anteorbital foramen a 

 vertical slit, widening above and bounded externally by 

 a broad plate of the upper maxillary; coronoid and 

 condyloid processes of lower jaw well developed. A 

 large family, found in all parts of the globe, some of the 

 species {Mus) being cosmopolitan, having accompanied 

 man in his migrations through the ages; all are of small 

 size, the muskrat being one of the largest, and many are 

 smaller than any other quadrupeds, except the Shrews. 

 * Incisors laterally compressed ; molars rooted. (MuKisriB.) 

 f Molars with three tubercles in transverse series; soles naked; 

 tail long, scaly ; (Old World species, introduced in America.) 



Mus, 1. 

 f f Molars complicated, witli two tubercles in transverse series ; 

 soles usually hairy; (New World species.) 

 a. Bat-like; size large; ears large, rarely naked. Nbotoma, 3. 

 aa. Mouse-like ; size small. 

 6. Incisors not grooved; ears very large; feet and lower 

 parts usually white. . . Hbsperomts, 3. 



6&. Size very small ; upper incisors grooved longitudinally 

 along their anterior surface. . Ochetodon, 4. 



** Incisors very broad; molars rootless (except in Evotomys). 

 X Tail not specially compressed ; teeth not grooved. 



