CASTOR. 159 
now become extinct in the majority of localities. Its skin and scent 
bags were too valuable commercially to preserve it from man’s 
rapacity. It is probably one of the best-known rodents in the land, 
and most persons have some knowledge of the beaver’s house and 
dam, or have seen the trunks of trees that have been cut down by 
the wonderful adze-like incisors. Clothed in a dense furry coat im- 
pervious to water, and provided with paddle-like hind feet and a broad 
rudder-like tail, the beaver is at home in the lake or river, where 
most of its life is passed. It shuns the vicinity of man, and exists 
only in the virgin wilderness. 
Fam. Il. Castoridze. Beavers. 
Skull massive, no postorbital processes, superior outline nearly 
straight; molars single-rooted, with re-entering of enamel folds, and 
decreasing in size posteriorly; the molar series is not parallel but con- 
verges anteriorly, and the palate is arched, contracted anteriorly. 
Incisors large, powerful, the lower much longer than the upper, with 
chisel-like edges, and a deep orange red color exteriorly.. Lower jaw 
massive; angle of mandible rounded. 
39. Castor. Beaver. 
Castor Linn., Syst. Nat., 1, 1758, p. 58; 1, 1766, p. 78. Type Castor 
fiber Linneus. 
Feet four-toed, hind feet large, webbed; upper molars subequal, 
with one inner and two outer enamel folds; tail broad, flat, scaly; 
molars with dentinal pulp persisting until quite late in life. 
canadensis frondator (Castor), Mearns, Proc. U. S. Nat. Mus., 
1897, p.502. Elliot, Syn. N. Am. Mamm., rgor, p. 116. 
SONORAN BEAVER. 
Type locality. San Pedro River, State of Sonora, Mexico, near 
monument No. 98, Mexican boundary. 
Geogr. Distr. From State of Sonora, Mexico, to Wyoming and 
Montana. 
Genl. Char. Size large; scaly portion of tail less than twice as 
long as wide. 
Color. Upper parts russet, chocolate at root of tail; under parts 
grayish cinnamon to ferrugineous beneath tail; sides wood brown 
varied with tawnyolive; feet burnt sienna. 
