500 PROCEEDINGS OF THE ACADEMY OF [1897. 



Philadelphia. In athabascce the relative length of the horns and horn- 

 cores to the size of the skull is about the same or even greater than 

 in antiquus, but on the other hand they are much more slender and 

 recurved than in B. bison. In their abrupt curvature they resem- 

 ble B. scaphoceras, but in their relative slenderness they are farth- 

 est from that species of any of our American species except the 

 straight and long-horned latij'rons. Judged solely by horn charac- 

 ters their place in the chronological series would appear to be the 

 latest of all our known species, with the minimum of calibre and 

 the maximum of curvature ; but the weight of evidence favors their 

 position between B. bison and the most recent fossil species. 



Below is given a list of the living and extinct species of American 

 bisons now recognized as valid, with their original references and 

 most important synonyms. The type localities, probable geographic 

 distribution and probable sequence in time are also given. Of the 

 fossil species the following were probably contemporaneous or closely 

 sequent: B. alleni, B.ferox n and B. scaphoceras in middle and later 

 Pliocene time ; B. alaskensis, B. latifrons and B. antiquus in earlier 

 and middle Pleistocene time; and " B. latifrons" (so-called, of 

 Leidy, from California) forming a connecting link in later Pleisto- 

 cene time with B. bison through B. bison athabascce. 



1. Bison alleni Marsh. Amer. Jour. Sci., 1877, p. 252 (= B. crampiamis Cope, 

 Jour. Acad. Nat. Sci. Phila., 1895, p. 456). 



Lower Pliocene of Kansas. Great Plains of Middle North Amer- 

 ica. 



2. Bison ferox Marsh. Amer. Jour. Sci., 1S77, p. 252. 



Lower Pliocene of Kansas. Great Plains of Middle North Amer- 

 ica. 



3. Bison scaphoceras (Cope). Jour. Acad. Nat. Sci. Phila., 1895, p. 457. 



Upper Pliocene of northern Nicaragua. Mountain regions of 

 southern Mexico and Central America. 



4. Bison latifrons (Harlan). Fauna Amer., 1825, p. 27.".. 



Pleistocene of eastern Kentucky. United States east of the Rocky 

 Mountains. 



5. Bison alaskensis Rhoads. Spec, nova (1. c.) (= B. crassicornia Richardson, 

 Zool. Voy. Herald, 1854 (in part), pp. 42 & 4:'.. PI. XIII, Bgs.. 1 & 2). 



Pleistocene of northern Alaska. Arctic America, east of the 

 Mackenzie River and north of the Arctic Circle. 



12 The status of ferox, especially in regard to its relations to latifrons, is hard 

 to determine. It is, however, close to latifrons, of which it probably was the- 

 nearest ancestor. 



