490 



REPORT OF STATE GEOLOOIST. 



t 



Family MURIDAE. 



RATS AND MICE. 



Size ranging from some of the smallest of mammals to the 

 muskrat, Which weighs several pounds. There is a single incisor 

 on each side of the upper and lower jaw ; no canines or premolars ; 

 molars three on each side of the upper and lower jaws. 



The family is of world wide distribution and includes over 

 100 genera and more species than any other family of mammals. 

 The tropical species, which are very numerous, are still imperfectly 

 known and many new species and genera will yet be found. 



The American rats and mice belong to four subfamilies which 

 can generally be very easily distinguished. To the Murinae belong 

 the introduced mice and rats which are all well-known household 

 pests. They are characterized principally by the long, scaly, nearly 

 hairless tails, and. by having the tubercles or projections on the 

 crowns of the molar teeth of the upper jaw arranged in three rows. 



The second group, Cricetinae, includes many old world species 

 and all of the white-footed mice, harvest mice, grasshopper mice 

 and others of North America. They have also moderately long 

 tails, slender limbs and bodies and many of them have white bellies, 

 large ears and prominent eyes. The tubercles of the upper molars 

 are arranged in two rows. 



The third group, Microfinae, includes the meadow mice or voles 

 and the muskrat. With the exception of the muskrat they all have 

 short tails, short legs, small eyes and ears and plump, thick bodies. 

 The crowns of the molars are without projecting tubercles, but are 

 flat and are arranged in a series of loops and triangles which project 

 from the middle line on both the inner and outer side of the teeth. 



The fourth group, Neotom'n^ae, includes the native cave rats 

 and wood rats, of which only two or three species are found east 

 of the ]\I ississij)])! and none have certainly been recorded from In- 

 diana. 'V\\v\' resemble th(^ house rat in external form, but the belly 

 is pui'e white, the tail is more thickly covered with hair and the 

 teeth bear considerable resembhmce to those of the Mivrotiuac. 

 They were formerly [)laced in the subfamily Criccthtae, to which 

 they are related, but more recently they have been regarded as 

 forming a separate subfamily. 



