THE MITSKRAT. 



517 



Genus Fjukr Cuvior. 

 Fiber Ciivier, Lefons d'anat. comp., Vol. I, tabl. 1, 1800. 

 Dental Formula.— J, C, Pm, ^Jz^; M, fEf = 16. 



Generic characters. — Distinguished from all other members of 

 the family by the large size and long tail, which is laterally flat- 

 tened. The skull and teeth resemble those of some of the larger 

 species of Microtus, but the molars are rooted. 



The genus is limited to North America, and extends from 

 northern Mexico to Labrador and Alaska. About ten species and 

 subspecies are now recognized. Only one of these occurs in Indiana. 



FIBER ZIBETHICUS (Linnaeus). 

 MUSKRAT. 



[Castor] zihethicus hum., Syst. Nat. Ed. 12, Vol. I, p. 79, 1766. 



[Fiber] zibethicus Cuvier, Regne Animal, Vol. I, p. 192, 1817. 

 Fiber zibethicus Evermann and Butler, Proc. Ind. Acad. Sci. 

 for 1893, p. 126. 



Diagnostic characters. — ^^Those of the genus. 



Description, — Fur of two kinds, an overfur of long, moderately 

 coarse hairs, and a dense underfur of wooly hairs. The color is 

 dark glossy brown above, with the sides tinged with yellowish and 

 belly dirty, yellowish white; upper lip yellowish. Hind feet very 

 broad, with the toes joined together by a web; ankle joint so con- 

 structed that the feet can be turned edgewise during the forward 

 stroke of the foot in swimming. 



The whole structure is a very perfect adaptation to aquatic 

 life. The tail acts as a rudder in the water; the feet make very 

 effective propellers ; and the fur is a water-proof covering through 

 which no moisture penetrates. 



Measurements. — An adult female from the Kankakee near He- 

 bron measured 640 mm. (25 10/16 in.) in total length; tail, 290 

 mm. (11 10/16 in.) ; hind foot, 75 mm. (3 in.). 



Skull and teeth. — The skull resembles that of the species of 

 Microtus in general appearance but, of course, is much larger, 

 The braincase is quadrangular as in M. pifietorum, but is not so 

 flat and the rostrum is proportionally longer. The roots of the 

 lower incisors are outside the roots of the molars. 



Range. — The typical form is found from southern Canada to 

 southern Virginia and. the Gulf States and west to at least the 

 Rocky Mountains. It is found in this State wherever there are 

 suitable bodies of water. 



