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MAMMALS OF MINNESOTA. 169 
- of head and and throat 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 noticezable 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 beep 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. 
Famity CASTORID. 
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 Muride. 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+ 
de are modified for aquatic life and seem to have descended 
from aquatic species. 
The Myomorphainclude 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 Chalicomys 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 
—11 
