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. 



= Jaculus, Wagler. 



1. Z. hudson/us, ( Zimmermann ) Coues. Yellowish 

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



FAMILY XIV. MURID^E. 



(The Mice.) 



Incisors f ; molars usually |:|; 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- (MURIN^E.) 

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

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



Mus, 1. 

 ff Molars complicated, with, two tubercles in transverse series ; 



soles usually hairy ; (New World species.) 

 a. Rat-like ; size large ; ears large, rarely naked. NEOTOMA, 2. 

 aa. Mouse-like ; size small. 



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



parts usually white. . . . HESPEROMYS, 3. 



bb. Size very small ; upper incisors grooved longitudinally 



along their anterior surface. . OCHETODON, 4. 



** Incisors as broad as deep ; molars rootless (except in Ewtomys). 



$ Tail not specially compressed ; teeth not grooved. 



