1894.] NATURAL SCIENCES OF PHILADELPHIA. 127 



in the British Museum, 295 mm. long, presents the flat frontal 

 outline and the relative width of the American black species, coupled 

 ^vith the extreme dentition of ardos. 



Skulls of americanus reach nowhere the extreme proportions of 

 citnmmomeus, nor in ordinary specimens is there much suggestion of 

 its outlines. Two remarkable skulls, however, in the collection of the 

 Academy (Nos. 2,756 and 2,757) from Sonoma Co., California, marked 

 "brown bear" reach an extreme of breadth and length of tooth, in this 

 species, with a frontal depression almost equal to that of cinnamomeus, 

 although in the Sonoma specimens the plane of the forehead is con- 

 tinuous nearly to the end of the nasals and is but slightly concave. 

 These two skulls are the most extreme of americanus which I have 

 ever seen, but while I would have been glad to examine more speci- 

 mens of these brown bears than have been within reach, I am 

 yet prepared to hazard the belief that fully matured specimens will 

 show, as compared with black ones, a sometimes slight but fairly con- 

 stant excess both in breadth and size of molar. 



There can be here no question of specific difference, both colors 

 being found in the same litter of cubs and the fact can be explained 

 only by regarding it as an evidence of reversionary tendency to a 

 brown- colored, large-toothed ancestor, — such as ardos ; the physio- 

 logical correlation between hair and teeth being well known. If, as 

 I believe, the foregoing suggestion should be found to hold good in 

 a large series, there is certainly a tendency in brown specimens of 

 americanus toward the characteristics of cinnamomeus, and here also, 

 perhaps, room may be found for the special features of the Louisiana 

 skulls in the National Museum which Dr. Merriam^" recently ascribed 

 to Ursus luteolus Griffith. 



From these observations the conclusion is drawn that if horribills 

 and americanus are to stand as good species, as distinct from ardos as 

 they undoubtedly are from each other, cinnamomeus must be con- 

 sidered as even a Ijetter one. But whatever the differences may be 

 among the American forms, taken by themselves, a comparison with 

 a large series of ardos, brings to light such a degree of instability 

 and intergradation, that the only philosophical vie^Y which can be 

 taken of their relationship is that expressed some years ago by Mr. 

 J. A. Allen" but subsequently abandoned by him,^- at least so far as 



101. c. pp. 147-152. 



" Bull. Mus. Comp. Zool., II, pp. 334-342. 



'2 Bull. U. S. G. & <l. Survey, II, No. 4, p. 340. 



