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The following monograph consists essentially of two quite distinct parts. 

 The first embraces descriptions of the species^ while the second is devoted to 



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the consideration of the geographical distribution of Bison americaniis. The. 

 first part of Part I, or that portion relating to the extinct species, is the least 



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satisfactory, owing to the scantiness of the materials for their description. 

 It has been my good fortune, however, to have the opportunity of examining 

 nearly all the material thus far described from the United States relating to 

 these interesting forms, including the original specimens of Bison Mifrons and 



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Bison antiquiis^ as well as the later-described bison remains from California. 

 The specimens from Eschscholtz Bay, described by Richardson, I have not 

 had an opportunity of seeing, but I have had access to a few remains 

 the extinct bison from other Alaskan localities. 



In the following pages two extinct species are recognized, which differ 

 quite widely from each other, the one {Bison Mifrons Leidy) being much 

 larger than the other {Bison cmtiqims Leidy = Bison crassicornis Eichardson), 

 with disproportionately larger horn-cores. Neither of the species is as yet 

 known from satisfactory material, although enough of their remains hav^ 

 been found to indicate the existence of two widely differing forms. Without 



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knowing positively more of Bison Mifrons than the three cranial frag-ments 



thus far discovered represent, it is difficult to assign some other specimens 

 to the one species rather than to the other, owing to our lack of knowledge 

 of the sexual difference in size this large species may present. The female 

 of the larger extinct species, judging from the sexual differences seen in the 

 living species, would apparently about equal in size the male of the smaller 

 one, and hence it is difficult to positively specifically assign such specimens 

 as detached teeth or single bones of the extremities. Ao^-ain, the female of 

 the smaller extinct species being of about the size of the male of Bison 

 americanus (perhaps a little smaller) still further complicates the problem. 



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