MAMMALS OF MINNESOTA. 169 



of head and and threat yellowish, chin and nose gray. Below, 

 especially about the fore legs, with much rusty red. Ears 

 rounded, rather large. Tail short, bushy, terete. Colors vary 

 greatly, with noticeable tendency to melanism. A patch of 

 white marks the lower lip and a more or less distinct bar of 

 gray crosses the muzzle. There is a curious callosity just 

 above the short upper incisors. The sole has six callosities, the 

 palm five. There are two pairs of pectoral and one of in 

 guinal teats separated by an interval of five inches. 



The woodchuck may be somewhat widely distributed in Min- 

 nesota but the only localities at which is has been encountered 

 are upon the tributaries of the St. Louis and the shores of lake 

 Superior. Here it does not appear to attain the size of the 

 eastern specimens and perhaps is more brightly colored, 

 though observations are lacking to support this statement. 

 The habits are exactly those of the Spermophiles including the 

 curiosity which makes them an easy prey to the trapper. 



An adult Ohio female measures as follows: Length, 14.50; 

 tail to end of hairs. 9.50; fore foot, 2.50; hind foot, 3.00; nose 

 to eye, 1.80; nose to ear, 3.70; hight of ear, 1.00; width of 

 muzzle, 1.15; distance between eyes, 1.90. 



FAMILY CASTOKID^E. 



This family is placed among the Sciuromorpha, thus express- 

 ing a relationship with the squirrels which is more completely 

 seen in internal structure than in externals. The family differs 

 from the squirrels in not possessing the postorbital frontal 

 processes and in the oblique positions of the molar series. The 

 teeth are imperfectly rooted and the enamel is folded, more as in 

 the Muridce. Some doubt may be expressed as to the correctness 

 of this reference, since in several characters the resemblance 

 is with the Myomorpha. The existing members of the Castori- 

 dce are modified for aquatic life and seem to have descended 

 from aquatic species. 



The Myomorpha include several aquatic species but, beyond a 

 superficial resemblance, even the muskrat has little in common 

 with the beavers. 



Beavers, not very unlike the existing species, made their ap- 

 pearance during the Miocene Tertiary. The genera Trogono- 

 therium in India Ghalicomys in Europe and Steneofiber and Eucastor 

 in America were companions of their more favored relative. The 

 Miocene was the period during which the rodents differentiated 

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