CASTOR. 



MURID^E. 



161 



FIG. XXXIV. CASTOR c. FRONDATOR. SONORAN BEAVER. 



The MuRiD^E is the largest family of the rodents and is cosmo- 

 politan, some members, such as the Brown Rat being met with 

 throughout the world, carried from place to place in ships. It includes 

 a vast number of genera, embracing both terrestrial and aquatic 

 animals of varied structure and habits, while the size of the numerous 

 species ranges from that of the pigmy Harvest Mouse (genus Rhithro- 

 dontomys) to that of the Musk-rat. Every land possesses its own 

 peculiar species, and North America has a large number indigenous 

 to it. They are of a great variety and are dwellers of the woods, 

 cultivated fields, prairie lands, swamps, lakes, and rivers, each seeking, 

 after its kind, localities best suited to its mode of life. 



The subfamily Murince is typified by the Rat and Mouse of our 

 houses, and these have their representatives in other subfamilies 

 of many varied forms and structures. Some are possessed of cheek 

 pouches. The tubercular teeth have their crowns worn by constant 

 use to a flat surface and they then exhibit various tracery patterns, 



