a few cases the difference is slight, as in kidderi of 

 Alaska Peninsula. 



AGE DIFFERENCES 



"Bear skulls undergo a series of changes from 

 early life to old age, and in most species do not at- 

 tain their mature form until seven or more years of 

 age. In species having the frontal shield highly 

 elevated, as in middendorffi, kluane, stikeenensis, 

 and mirabilis, the frontals reach their maximum of 

 arching or bulging in early adult life (about the 

 sixth year), after which they gradually become 

 flatter. ... 



"classification of grizzly and big brown bears 



"The differences formerly supposed to exist be- 

 tween the grizzlies and the big brown bears appear, 

 in the light of the material now available, to dis- 

 tinguish certain groups of species from certain 

 other groups, rather than the grizzlies collectively 

 from the big brown bears collectively. In other 

 words, the differences between the grizzlies on the 

 one hand and the big brown bears on the other are 

 neither so great nor so constant as at one time be- 

 lieved. And there are species which in the present 



261 



