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state of knowledge cannot be positively referred to 

 either group. In fact, it seems at least possible that 

 certain species which appear to belong with the 

 grizzlies are closely related to certain other species 

 which clearly belong with the big brown bears. The 

 typical brown bears differ from the typical grizzlies 

 in peculiarities of color, claws, skull, and teeth. 

 The color of the former is more uniform, with less 

 of the surface grizzling due to admixture of pale- 

 tipped hairs; the claws are shorter, more curved, 

 darker, and scurfy instead of smooth; the skull is 

 more massive; the fourth lower premolar is conical, 

 lacking the sulcate heel of the true grizzlies. But 

 these are average differences, not one of which 

 holds true throughout the group. Most of the spe- 

 cimens in museums consist of skulls only, unac- 

 companied by skins or claws, leaving a doubt as to 

 the external characters; and in old bears the im- 

 portant fourth lower premolar is likely to be so 

 worn that its original form cannot be made out. 

 And, worst of all, some of the grizzlies lack the dis- 

 tinctive type of premolar, leaving only the skull as 

 a guide to their affinities. The present classification, 

 therefore, must be regarded as tentative and sub- 

 ject to revision. . . . 



262 



