52 RODENTS OP IOWA 



Big Creek, North Tama county, for eight years past, but not a 

 trace of them conld be found last fall."^ 



Doubtless many other records of the occurrence of this rodent 

 in different parts of the state could be collected ; but they would 

 serve no useful purpose so far as the object of this paper is con- 

 cerned, and those above given will suffice. 



RATS AND ]\nCE. 



Family MURID^E. 



The Muridffi is the largest family of rodents and, indeed, of the 

 whole class of mammals, as it numbers over five hundred forms. 

 The family is cosmopolitan in distribution, and some forms such 

 as the brown rat are met with throughout the world, having been 

 carried from place to place in shipping. Every country, including 

 North America, has its own peculiar species. Both terrestrial 

 and aquatic forms are found in the family. Various localities and 

 habitats are chosen according to the mode of life ; and swamps, 

 lakes, rivers, prairies, cultivated lands, and woods all have their 

 representatives. In size the members of the family vary from the 

 small harvest mice to the muskrat, the largest representative otf 

 the family. 



HOUSE MOUSE. 



31 us miisculus Linnaeus. 



[Mus] musculus Linnanis, Syst. Nat., X ed., I. 62, 1758, 



Description. — Color above dark brown grading to lighter brown 

 on sides of body; color below grayish brown, but without distinct 

 line of demarcation between color of this part and that of sides ; 

 tail dusky, scantily haired and longer than body ; feet grayish 

 brown. 



Measurements. — Total length, 6.75 inches; tail vertebra?, 3.15 

 inches ; liind foot, .75 inch. 



This form may be distinguished from our other small mice by 

 the grayish brown under parts, the size, the length of tail, and the 

 fact that the molars or grinding teeth have the tubercles on the 

 crowns arranged in three longitudinal rows. 



Uabits, Distribution, Etc. — The house mouse is a species intro- 

 duced into this country from Europe, arriving soon after the first 

 American settlements Avere established. It now inhabits all the 



'Nutting, C. C, Proc. la. Acad. Sci., I, pt. Ill, 40, 1892. 



