1896.] ^^^ [Farr. 



are too large for M. intermedius, and their provisional reference to 

 J/, copei is justifiable. These are very like those of M. hairdi, but much 

 larger and more massive. The provisional reference of the two pre- 

 molars described with the type is also justifiable, as they are too large 

 to pertain to any other known species of horse from the White River. 

 Leaving the pelvis out as questionable, we may say that the remains in- 

 dicate a very large equine agreeing with M. bairdi in most of its charac- 

 ters and yet specialized in its own way so that it is a little ofl:" the line of 

 equine descent though most probably developed from M. bairdi. 



Measurements of M. copei. 



MM. MM. 



Tibia 298 313 



Calcaneum, length 83 



Calcaneum, extreme width 30 



Astragalus, len gth 46 50 



Astragalus, width of neck 31 37 



Height of navicular 11 



Height of ecto-cuneiform 11 



Length of M. iii 177 189 



Femur, distal end width 51 



Width of patellar surface 29 



Extreme length of first phalanx of M. iii 24 



" " second " " 11 



" " ungual " " 29 



Length of M. iv 155 



Phalanx 1 of M. iv 14 



2 " 9 



3 " 22 



Mesohippus intermedius O. and W. 



M. intermedius, as the name indicates, stands intermediate between 

 J/, bairdi of the Oreodon beds and Mesohippus {Anchitlierium) proestans 

 of the John Day. It occurs in the Protoceras beds. It is a strange and 

 interesting fact that M. bairdi continued on into the time of the Protoceras 

 beds after having given rise to the two species.* A careful study of the 

 principal characters of M. intermedius brings out very strongly its rela- 

 tion to the preceding and succeeding species. In all these points it is 

 seen to stand directly intermediate between M. bairdi and Mesohippus 

 (Anchitherium) priestans of the John Day. In the light of present 

 knowledge there can be no doubt that M. bairdi is the direct ancestor of 

 the modern horse, and by the study of the individual variations of the 



* A remarkable instance of the persistence of an ancestral type is seen in the Loup 

 Fork. Here Protohippus, a form with long-crowned, cement-covered molars, represents 

 the main line of equine descent, while right alongside of it there is a much smaller spe- 

 cies of M. bairdi type which Cope has called Anchitherium uUimuni. This form has short- 

 crowned molars, without cement. 



