335 



Measurements of seventeen skulls of URSUS ARCTOS (chiefly sulsp. HORRIBILIS). 



The question of the relationship of the large Bears of Forth America 

 to those of the Old World has long been a vexed one, and is, of course, 

 one not easily settled. In the present collection are thirty-three skulls, 

 representing various ages, but the greater part are adult. These in- 

 clude two only from the Old World, six from the Arctic coast, eleven 

 from California, an'd fourteen from various localities in the Eocky Mount- 

 ains, from Idaho Territory to Arizona. 



Among the American specimens are two rather easily distinguishable 

 forms, one of which is the large Grizzly, or U. liorribilis of authors, from the 

 western parts of the United States ; the other, the smaller so-called Bar- 

 ren Ground Bear of Arctic America ; both being undoubtedly specifi- 

 cally distinct from the Ursus americanus. The Barren Ground form* 

 differs from the more southern Grizzly not only in its smaller size, but 

 in its strong tendency to a depression of the frontal region of the skull, 

 where the simple flattening of this region in the Grizzly is here often car- 

 ried so far as to form a well-marked concavity as in the true arctos of 

 the Old World. Sometimes, 'however, U. horribilis also presents a con- 

 siderable depression between the postorbital processes, as great even as 

 in average specimens of U. arctos, as is the case in No. 7401 from Mon- 

 terey, Cal. The Barren Ground Bear's skull generally presents a 

 more dog-like aspect, in consequence of the thickening superiorly of 

 the postorbital border of the frontals, than is seen in U. liorribilis , it 

 approaching in this respect to the form seen in Ursus spelceus, where this 

 feature attains its highest development, resulting in the very strong 

 frontal depression so characteristic of the skulls of that species. 



The dentition of U. arctos, U. richardsonij and U. horribilis presents 

 no important differences, the chief difference being the relatively rather 

 smaller size of the teeth in the latter. The form of the last upper molar 

 is almost precisely the same in the two first named, and the differences 

 presented by U. horribilis are both slight and inconstant. In U. rich- 

 ardsoni, this .tooth narrows gradually, and about equally, on each side 

 posteriorly, almost exactly as in U. arctos , it being widest at or near its 

 extreme anterior border. While this is sometimes the case in U. horri- 

 bilis, its greatest breadth is generally one-fifth the length of the tooth 

 behind the anterior border, and the tooth is relatively broader posteriorly 



* Named by Captain Mayne Reid, in one of his stories, " Ursus Eichardsoni" ! 

 t The Barren Ground Bear skulls in the collection are labeled with this name. 



