MAMMALS URSIDAE URSUS HORRIBILIS. 223 



The skull of the grizzly hear can at all times he distinguished hy its size alone from all other 

 American species, excepting the polar hear. This, however, differs exceedingly in many respects ; 

 the muzzle is much hroader and more arched ; the nasal bones extend further backward. The 

 base of the whole skull is much curved from the condyles to the incisors ; the palate being 

 excavated almost into a boat shape. Thus, a straight line extended from between the occipital 

 condyles to the crowns of the incisors will pass more than 1 inches above the centre of the 

 palate ; in the grizzly bear not half an inch. The head of U. maritimus is much narrower, 

 being barely more than half as wide as long. The zygomatic arches are lower and weaker. 



The teeth of the polar bear, with the exception of the canines and incisors, are much smaller 

 than in the grizzly, scarcely exceeding, in absolute dimensions, those of the common black bear. 

 The posterior upper molar is smaller than in the average of U. americanus, and quite similar in 

 shape ; the posterior half of the crown is nearly horizontal. The third molar from above is 

 much more truly pectorial than in other bears ; the anterior lobe being much longer than the 

 posterior, which is reduced to a smaller size. The horizontal section of the tooth is sub-elliptical, 

 not triangular, and the inner tubercular lobe seen in most other species is here reduced to a 

 basal ridge. There are also differences of importance in the lower molars in the nearly horizon 

 tal and plane crowns of the very small posterior one, the fewer tubercles of the others, the 

 absence of distinct vertical wrinkles on the outer surfaces, &c. The incisors also differ mate 

 rially. It is not necessary, however, to push further the comparison of the species. 



The relationships existing between the skulls of Ursus horribilis and U. arctos of Europe are 

 pretty close. Although our species is considerably larger, De Blainville, in his " Osteographie 

 Comparee," as well as other authors, considers it to be a mere variety of the U. arctos, forgetful 

 of the dogma of Buffon that the species of the New World are in general merely degenerate 

 varieties of those of the Old. I have not had the opportunity of examining an adult head of 

 U. arctos, but the oldest and largest figured by Blainville measures 14 inches in length and 

 9.3 inches in width. Thus, while the length is somewhat less, the width between the zygomata 

 is much greater, being 0.66 of the length. In the broadest skull of U. horribilis before me, 

 and one agreeing in age with Blainville's specimen, the proportion is but 0.61. This width of 

 head far exceeding that of any well known American species, would appear to be quite conclu 

 sive as to the question of identity. Another skull of U. arctos, as represented in the " Oste 

 ographie," is 11.40 inches long and 7.50 inches wide, or in the proportion of 100 to 66 nearly. 



In comparing a skull of the grizzly bear of California (1220) with one of U. arctos from 

 Sweden, marked two years old, (No. 1033,) I find them both of nearly the same relative age, 

 the latter a little the most forward. The last upper molar has made its appearance in both, 

 the last lower one has its crown four-fifths exposed in U. arctos; in the other, with one-third 

 visible, but not yet above the alveolus. The deciduous canines have not yet fallen in either ; 

 the outer upper incisor is not quite up in the California specimen, while it is nearly in place in 

 the other. In these specimens the greater breadth but smaller size of the European bear is 

 distinctly evident. The teeth are proportionally larger in the American animal ; the posterior 

 half of the last upper molar more horizontal and broader, the outer surfaces more wrinkled. 

 The sectorial molar above is much broader in the grizzly, being nearly as wide as long, though 

 sub-triangular in shape. In U. arctos this molar is proportionally longer, and little more than 

 half as wide as long ; the inner tubercle is much smaller, and in the more trenchant and com 

 pressed crown, and higher anterior lobe, resembles quite closely the corresponding tooth in the 



