192 



BULLETIN NO. VII. 



The eastern Michigan mouse although much less bright than 

 H. leucopus has on the sides a decided brownish cast, or even 

 fawn color, while the typical western variety has scarcely a 

 trace of any other tint than black and white except on the up- 

 per surface of the tail. About the head there is the same hoari- 

 ness exhibited by other prairie mice, as though faded by the 

 sun. As a rule there is a less sharply defined line of demarka- 

 tion between back and belly than in more eastern specimens 

 examined. 



In all the Michigan mice examined the ear is white -rimmed 

 in spite of Dr. Coues' assertion to the contrary. Although the 

 dorsal dark area may not reach the hand there is invariably a 

 dark blotch on the wrist which may or may not embrace the 

 whole upper surface of the hand. 



The following table of measurements, of which all but the 

 last two refer to specimens captured near the western line of 

 Minnesota, may show the variations in size and can be taken 

 as fully trustworthy, having been made with great care from 

 fresh specimens: 



SUBFAMILY ARVICOLIN^E. 



The field mice, which are included in this section of the 

 immense rat family, may be readily recognized, as a rule, by 

 their rather clumsy and squatty form, blunt muzzle and small 

 ears. Tail and limbs are generally short, while the eyes are 

 small. The fur is often thick and fluffy, while the colors are 

 predominatingly rusty brown. The north temperate regions 

 of both hemispheres form the habitat of the majority of the 

 species. None occur in South America. As in other northern 

 mammals, there is rather a close conformity between the faunae 

 of Europe and America. 



The anatomical characters are no less conspicuous. The 

 incisors are broad and short. The molars are perfectly pris- 

 matic, and their growth is continuous, so that after the crowns 



