THE AMERICAN BISONS. 25 



correctness of this reference. This specimen (see Plate IV) embraces the 

 upper surface of the skull except the nasal bones, but lacks the occipital and 

 lower surfaces, including the teeth and the greater portion of the maxilla?. 

 It belonged to a rather young or middle-aged animal, in which the sutures 

 had not closed. This specimen is remarkable for the flatness of the frontal 

 region, which is not elevated above the plane of the base of the horn-cores. 

 As this degree of flatness is nearly equalled in recent specimens of B. ameri- 

 camis, among which the range of variation in respect to the convexity of the 

 frontal region is very great, it forms a difference of no great importance. 

 The only prominent difference between it and corresponding specimens of 

 B. americamis, is in the disproportionately large size of the horn-cores. The 

 general dimensions of the skull (see Table IV) are not larger than those of 

 large old male specimens of B. americamis, but the horn-cores are one third to 

 nearly one half longer and proportionately thicker. The horn-core of a 

 bison from the Tatlo River, Alaska, obtained by Mr. Dall, almost exactly 

 corresponds in size with the one from St. Michael's (compare columns 3 and 

 7 of Table IV). They agree also very nearly in size with the specimens 

 doubtfully referred by Dr. Richardson to Bison prisons (see columns 1 and 2 

 of Table IV). They differ from Richardson's B. crassicomis very much as 

 the female of that species might be expected to differ from the other sex. 

 There are in Alaska certainly the two forms, which may be only male and 

 female of one and the same species, or quite distinct species, the smaller of 

 which would present an almost exactly half-way link between the larger B. 

 "crassicomis " of Richardson and the existing B. americamis. If there are two 

 species we as yet know only the males of each, and it therefore seems more 

 reasonable to regard the two forms as different sexes of the same species. 



Considering the above-mentioned remains as conspecific they seem to in- 

 dicate a species of much larger size than the existing American bison, but 

 one not essentially differing from it in form. The older and larger is most 

 evidently the direct and not very remote progenitor of the existing Ameri- 

 can bison. 



Its affinities are perhaps also as close with the existing aurochs as with 

 the latter. The chief differences, so far as its few known remains will permit 

 one to judge, between the species here recognized as Bison antiquum and the 

 existing species of bison, consist in its larger general size, and in the dispro- 

 portionately larger size of its horn-cores. As shown by the following table 

 of comparative measurements of the horn-cores and skulls of all the hitherto 



