CASTOR. MURID#&. 161 
FiG. XXXIV. CASTOR C. FRONDATOR. SONORAN BEAVER. 
The Murtip# 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 placein 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 //uthro- 
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 Murine 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, 
