RODENTIA—CASTORINAE—CASTOR CANADENSIS. 355 
CASTOR, Linnaeus. 
Castor, ‘* Linnaxzus, Systema Nature, 1735.’ 
Aup. & Bacu, N. Am. Quad. I, 1849, 347. 
A double claw on the second hind toe. Hind feet webbed. Tail broad, flat, and scaly. Molars 4=$, complicated or 
folded, with one groove on the inner side of each upper molar, and three on the outer, and vice versa below, (the anterior 
molar sometimes with more.) 
As we have but one species of North American beaver, I shall not stop here to go into more 
detail concerning the characters of the genus, but refer for these to the succeeding pages, where 
they are given in combination with those that are perhaps more specific. 
The systematic position of the genus Castor has long been a matter of considerable uncertainty. 
By some authors it has been placed in a distinct family, composed of Castor and Myopotamus. 
The last mentioned genus, in everything but external form is, however, most closely allied to 
the Hystricinae, while the beaver in many points of structure is closely related to the Sciuridae, 
especially to the spermophiles; and it may, therefore, without undue violence be placed as a 
sub-family of the Sciwridae. The general resemblance in shape between the skull of the beaver 
and that of some of the spermophiles, as S, /udovicianus, is indeed quite striking ; the form and 
relations of the malar bones and the ante-orbital foramen are much the same in both. 
CASTOR CANADENSIS, Kuhl. 
American Beaver. 
Castor canadensis, Kuun, Beitrage zur Zoologie, 1820, 64. 
Fiscuer, Synopsis, 1829, 288. 
*€ Castor americanus, F. Cuvier, Histoire des Mammif. 1821.’’ 
i Branopr, Beitrage Kennt. Saugt. Russlands, 1855, 64; pl. i, ii, iii (figures of tail and skull). 
Castor fiber, Say, Long’s Exped, R. Mts. I, 1823, 464. 
Haran, F. Am. 1825, 122. 
Gopman, Am. N. H. Il, 21. 
Dovueury, Cab. N. H. II, 1833; pl. i. 
Warernovse, Charlesw. Mag. N. H. II, 1839, 598; (figure of skull.) 
DeKay, N. Hist. N. Y. I, 1842, 72; pl. xx, f. 1; pl. viii, f. a. b. 
(Americanus,) Ricuarpson, F'. B. Amer, I, 1829, 105. 
Wacener, Suppl. Schreber, IV, 1844, 7. 
Aup. & Bac. N. Am. Quad. I, 1849, 347; pl. xlvi. 
Castor beaver, Pennant, Hist. Quad. 1781, No. 251.—Is. Arctic Zool. I, 1784, 98 ; (Leverian Museum). 
Le castor du Canada, Gorrr. & F. Cuvier, Hist. Nat. des Mammif. III, 1819, plate. 
The specimen from which the following account of the external form has been taken is quite 
young, measuring one foot in length to end of tail, and was preserved entire in alcohol. 
The general form of the beaver is that of a depressed ellipsoid, tapering almost equally to 
the head and the scaly portion of the tail. 
The head is large and broad; the muftle is naked ; the hinder border, or line of separation 
from the hairs of the forehead, is slightly concave anteriorly, and falls considerably behind 
the nostrils, (in the small specimen described five lines from the tip,) ard the space all round 
the nostrils is naked. The nostrils are lateral and widely open. The antero-inferior border of 
