40 THE AMERICAN BEAVER. 



pendent of Castor — have been ascertained, and that 

 the existence of its distinctive type extends backward 

 well toward the earliest epoch of mammalian life 

 upon the earth, yet it seems that the position of this 

 family in the animal kingdom is not as yet fully 

 determined. Whether the Castoridse are entitled to 

 the full rank of an independent family, or should be 

 attached, as a sub-family, to some other group, is the 

 question. 



Brandt, whose treatise upon the rodents is particu- 

 larly elaborate with reference to the beaver, gives 

 prominence to this question, and also to that of 

 the specific differences between the European and 

 American beavers. He proposes to divide the ro- 

 dent order into four sub-orders, and to arrange the 

 genera in twelve independent families. Under this 

 classification the Castoridse become an independent 

 family of full rank. " The general structure," he ob- 

 serves, "and especially the character of the skull 

 being more accurately considered, the order of the 

 Gnawers manifests, as it seems to me, four quite dis- 

 tinct types, exhibiting the equivalent of the sub-orders 

 Sciuromorpha, MijomorpJia, Hystricliomorplia, and La- 

 gomorplm, of each of which respectively the common 

 genera Scinrus, Mus. Hystrix, and Lepus, known to 

 all, may be declared the foundations. The four types 

 just indicated appear by no means to be constantly 

 separated by ascertained differences, but they rather 

 offer, by means of common marks and intermediate 

 forms, a series bound in unity with sufficient con- 

 cord."^ The Castoridx are placed in the second sub- 



^ " Strnctura general! et prassertim cranii ratione accuratius con- 

 sideratis Glirium Ordo typos quatuor admodum distinctos, ut mihi 



