122 University of California Publications in Geology [Vol. 9 



added a species to those described by Lucas, though apparently not 

 recognizing some of the described species. 



This wide difference of opinion may be attributed largely to the 

 diverse beliefs regarding the extent of individual variation and of 

 sexual dimorphism in the various members of the groups, this in turn 

 being due to the incompleteness and more or less fragmentary nature 

 of the material which could be referred with certainty to any particular 

 extinct species. 



In the collections of the Department of Palaeontology of the Uni- 

 versity of California there is a comparatively large series of skulls of 

 Bison antiquus from a number of localities in the Pacific Coast region 

 of North America, all, so far as known, of Pleistocene age, and repre- 

 senting, without any reasonable doubt, a single, well-defined form. It 

 is hoped that descriptions and comparative measurements of some of 

 these specimens will throw light on the problem of relationships of 

 the species. 



Individual and Sexual Variation in Existing Species 

 Due to the dissociation of parts, and the fragmentary nature of 

 most of the specimens which have hitherto been found the classifica- 

 tion of extinct bison has been based largely on the skull and horn- 

 cores, which afford very good comparative characters, but to what 

 extent they represent individual, sexual, or specific distinctions, has 

 been disputed. 



Before advancing evidence furnished by the fossil specimens, it 

 seems advantageous to summarize our knowledge of the variation in 

 existing species. 



BISON BISON (Linnaeus) 



As shown by Dr. J. A. Allen 5 in his memoir on the American bison, 

 the range of individual variation in the skull of B. bison is considerable, 

 much greater than that usually found within a single species, such 

 variation affecting the amount of convexity of the skull, shape of horn- 

 cores, size, relative measurements, etc. 



The size in adult male specimens, according to measurements given 

 by J. A. Allen, has a variation of about 20 per cent, the relative 

 measurements being subject to a less degree of variation. The range 



s Allen, J. A., Mem. Harv. Mus. Comp. Zool., vol. 4, no. 10, 1876, pp. 1-246, 

 12 pis., 1 map. 



