72 VERTEBRATES : MAMMALS. 



The Genus Mus Rats is characterized by upper 

 divided lips, acute snout, whiskers in five series, large 

 and nearly naked ears, and long tail, the scaly whorls of 

 which are very distinct. Over fifty species of this genus 

 are known, four of which have taken up their abode in 

 the United States. 



The Norway or Brown Rat, M. decumanus, Pallas, is 

 eight to ten inches long to the tail, which is somewhat 

 shorter .than the head and body ; the color above grayish- 

 brown mixed with rusty, beneath ashy white. This rat 

 is known all over the world, and is very destructive in its 

 habits. It belonged originally to Central Asia ; crossing 

 the Volga in large troops in 1737, it stocked Russia, and 

 subsequently overrun all Europe. In 1775 it found its 

 way to North America. It is often called Wharf Rat. 



The Black Rat, M. ratttis, Linn., is readily distinguished 

 from the Brown Rat ; its color being sooty-black above, 

 passing into dark plumbeous or paler beneath. Its origi- 

 nal locality is unknown. It has been the house-rat of 

 Europe from 'earliest times, and was introduced into 

 America in 1544. This species is rare, or wholly want- 

 ing, in localities where it was formerly very abundant ; 

 for it always disappears before its more formidable rival, 

 the Brown Rat. Both these species devour everything 

 edible that they can secure, often capturing living prey. 



The Roof Rat, or White-bellied Rat, M. tectorum, Savi, 

 of the Southern States, is smaller than the Brown Rat. 

 It is originally from Egypt, where it frequented the 

 thatched roofs of the houses ; hence its name. 



The House Mouse, M. musculus, Linn., originally from 

 Europe and Asia, but now found all over the world, is 

 grayish-brown, finely lined with darker, passing into ashy 

 plumbeous, with a reddish tinge on the belly ; the feet 

 are ashy brown. 



The Genus Cricetus, comprising the Hamsters of North- 



