30 UNITED STATES AND MEXICAN BOUNDARY. 



I am not aware that any direct comparison has ever been made between the skius and skulls 

 of the black bears of the eastern United States and those of the Eocky mountains and the I 



Pacific slope. It is quite possible that they may be really distinct, and that the western species 

 occurs in the black and brownish varieties, which would substantiate the impression that these 

 two colors in that country belong to one and the same species. There is at any rate no essential 

 difference between the skull of the ^^ black bear'' of the Copper mines and the brown bears 

 from the same localities, all exhibiting the same characteristic features as distinguished from 

 the black bear of eastern America. The black variety, however, appears to be much the rarer 



of the two. 



Skull. For reasons already explained I shall select a middle aged skull to serve as the type 



of my description, and afterwards point out the differences of the very young and very old 



specimens. Number 994, the head of a female from the Copper mines, has the tubercles of the 



molars and the crowns of the incisors considerably worn, so as materially to obscure their 



characteristics, while in a skull of U. americaniis of the same age the molars are perfectly entire. 



The sagittal crest extends over a little more than the posterior third of the parietal bone. 



The profile of the head exhibits a very decided convex curve from the occiput to the middle 



of the nasal bones, after which it passes off nearly horizontally, curving downwards towards 



the tip. 



more convex than in U, americanus^ rising higher in the 



middle. The central region of the forehead from the coronal suture to the middle of the nasals 

 is nearly plain or slightly convex, rounding off gently on the sides and to the tip of the post- 

 orbital process of the frontal bone. 



The outline from above exhibits a much greater breadth between the zygomatic arches than 

 in the skull of black bear described (897), which is, moreover, a little older. Thus the greatest 

 breadth is .617 of the total length, instead of .573. The projection of the end of intermaxillary 

 beyond the end of molar is .316 of the total length • the least width between orbits is .227 ; the 



distance between the tips of the orbital processes is .34. 



The lower jaw exhibits a decided character in the shape of its coronoid process. In this the 

 upper end curves round into a decided hook, the posterior outline being very much emarginated. 



Larger and older specimens exhibit a still greater breadth of head, amounting to as much as 

 .629 hundredths, while still older heads of the black bear are but .597 hundredths. 



This species, as already stated, differs very much in the width of the head from Ursus 

 americanus] the width of the head being at all ages (except in the very young) more than six- 

 tenths the total length in the one and less than this in the other. The upper edge of the 

 zygomatic arch is a good deal more curved. The lower jaw exhibits a striking character in the 

 great concavity of the hinder edge of the coronoid process, instead of the gentle curve of U. 

 americanus. 



There is quite an appreciable difference between the two species in reference to the anterior 



^ 



outline of the glenoid cavity. In one these outlines are in the same straight line, while in U. 

 americanus they diverge anteriorly, so as to meet at an obtuse angle if produced backwards and 

 inwards. 



The molar teeth of TJ, clnnamoneus are much smaller than in U. americanus. Thus the three 

 posterior npper molars in the largest specimen of cinnamoneus measure but 2.07 inches, the 

 others less than two inches ; in the smallest of americanus 2.22, in the largest 2.35. 



