466 



MAMMALIA. 



Protohi^ijioii in America, whose foot resembles that of Hip- 

 jiurion — the existing genus Equus not aiipiaiii'g until 1 ost- 

 PHooene times. 



3 3 3 



241.— Skeleton of Foot in various forms of Eiii ii>.4-„ 



A, fh'jhlppns (Encene); B, Aiichithrri'im (Upper Eocene and Lower and Upper Mio- 

 cene); c, Hipj^firicn (Upper Miocene and Pliocene); d, Equus (PVocene and Recent). 

 (Nicholson, idtrr Marsh.) 



There seem to he two distinct lines of descent, one in America 

 and one in Europe. In America the stages are Eohippos, 

 Orohippos, Mesohippos, Miohippos, Protohippos, Pliohippos, 

 and Equus. In Europe, Hyracotherium, Palseotherium, Anchi- 

 therium, Hipparion, and Equus.^ 



' Tlie living and extinct horses are tabulated as follows by Dr Gadow : — 



Eqiiidfr. Lower molars quadrituberculate, or with two transverse 



ridg&s curved into two half-moons. Toes, 4^, |, or \. Since Eocene. 



Hyracotherium 



Eohippos 



Palieotherium 



Mesohippos 



Auchitherium 



Hipparion 



Protohippos 



Pliohippos 



Hippidion 



Equus 



Toes, - 



Toes, 

 Toes, - 

 Toes, - 

 Toes, - 



Lower Eocene, England. 

 Lower Eocene, Wyoming. 

 r Eocene to Miocene, Europe and U.S.A. 

 Toes, f.-j Lower Miocene, Dakota. 



\ Upper Miocene of Europe = Miohippos, U.S.A. 

 Toes, f. Upper Miocene of Europe, Asia, and U.S.A. 

 |. Pliocene, U.S.A. 

 1. Pliocene, U.S.A. 



Pleistocene, S. America. 



Since Miocene in India ; since Pliocene in 

 Europe. During Pleistocene cosmopolitan, 

 excluding Australian region. 

 (' Classiiication of Vertebrata,' p. 47.) 



