LÖNNBERG, STUDY OF THE VARIATION OF EUROPEAN BEAVERS. 



outer. In the second very large 

 skull the following molar pattern 

 is to be found, lef t side : p^, the 

 two folds in question are obli- 

 quely opposite (half way »Elbe Rjgi^^ ^ppg,. fiolår series of an 



type»); m\ the inner enamel fold adult Beaver o^ from Elbe (inner 

 t ,1 , 1 i. 1 j j side up on the fig., p^ to the left 



large, the outer detached and side of the fig., m« to the right). 

 represented by a small isolated 



elliptical ring (column) of enamel; m^, the two folds opposite 

 (»Elbe type»); m^, the inner fold shoots past the end of the 

 outer (»Swedish type»). In all the molars, mS m^ and m^ 

 the posterior outer fold is fuUy detached from other enamel 

 layers and forms a free transverse enamelfold. The molars 

 of the right side quite are similar to the corresponding ones of 

 the left side, the outer posterior enamel fold being free and 

 even the anomaly of m^ being repeated. It is thus evident 

 that even the Elbe Beavers of the present day do not con- 

 stantly exhibit such an arrangement of the enamel folds as 

 Matschie has believed them to do, and in consequence they 

 are not to be distinguished from the Swedish ones by this 

 characteristic. The third characteristic which should distin- 

 guish the Swedish Beaver according to Matschie is that it 

 should ha ve the nasals »schräg nach vorn abgeschnitten». 

 This statement is founded on Meve's figure quoted which, 

 however, I regret to say, lacks in accurateness in this respect 

 as well. All Swedish Beaver skulls have the nasals emargi- 

 nated at their anterior end in the same way and the same 

 degree as the Elbe Beaver skulls, »so dass ihr Vorderrand 

 von der Seite gesehen winkelig ausgeschnitten erscheint». 



There does not remain anything of the three characte- 

 ristics on which Matschie based the distinction of the Elbe 

 Beaver from the Swedish Beaver. The question rises then 

 if possibly any other characteristics could be found con- 

 spicuous and constant enough to maintain such a difference. 

 It must then be born in mind that the growth of a Beaver 

 is continued during a very long period, perhaps during the 

 whole lifetime, and grow^th is always combined with more or 

 less pronounced changes, not only in size but in proportions 

 as well, and in consequence of this fact, great care must be 

 taken in selecting characteristics that really are constant. 

 An example of such changes during growth may be mentioned. 



