HISTORY OF THE PERISSODACTYLA 291 



matippus, mid. Mioc. f Hypohippus, mid. Mioc. to low. Plioc. 



fMerychippus, mid. Mioc. to low. Plioc. '\Protohippus, up. Mioc. 



fPliohippus, up. Mioc. and low. Plioc. \ Neohipparion, up. Mioc. 



and low. Plioc. \ Hipparion, Plioc. ^ Hippidion, Pleist., S. Amer. 



^Hyperhippidium, Pleist., S. Am. Equus, Pleist., N. and S. Amer. 

 II. ITiTANOTHERiiD^. fTitanotheres. 



\ Lambdotherium, low. Eoc. '\ Eotitanops, low. Eoc. \Pal(Eosyops, 



mid. Eoc. \Telmatheriwn, mid. Eoc. '\Dolichorhinus, up. Eoc. 



\Diplacodon, up. Eoc. \Titanotherium, low. Oligo. 

 III. Tapirid^. Tapirs. 



\Systemodon, low. Eoc. ^Isectolophus, mid. and up. Eoc. fPr'o- 



tapirus, Oligo. \Tapiravus, mid. Mioc. Tapirus, Pleist., N. Amer., 



Pleist. and Recent, S. Amer. 



IV. fLoPHiODONTiD.E. fLophidouts. 



^ Heptodon, low. Eoc. '\ Helaletes, mid. Eoc. '\Colodon, low. Oligo. 



V. Rhinocerotid^. True Rhinoceroses. 



\Trigonias, low. Oligo. \C(Bnopus, Oligo. and low. Mioc. fDice- 

 ratherium, up. Oligo. and low. Mioc. \Aphelops, mid. Mioc. to 

 low. Plioc. \Teleoceras, mid. Mioc. to low. Plioc. 

 VI. tHYRACODONTiDJE. fHyracodouts and fAmynodonts, cursorial and 

 aquatic Rhinoceroses. 

 ^Hyrachyus, low. and mid. Eoc. \Triplopus, mid. and up. Eoc. 

 \Colonoceras, mid. Eoc. f Hyracodon, low. Oligo. ^Amynodon up. 

 Eoc. ^Metamynodon, low. Oligo. 



Suborder fANCYLOPODA. tClawed Perissodactyls 

 VII. t Chalicotheriid.e. Chalicotheres. 



^Moropus, up. Oligo. and low. Mioc. 1 \Sckizotherium, low. Oligo. 

 '\Eomoropus, mid. Eoc. 



The earliest perissodactyls of which we have any knowl- 

 edge are found in the older part of the lower Eocene (Wa- 

 satch stage) of Europe and North America, into which they 

 must have migrated from some other region yet unknown, 

 for no probable ancestors of the group are found in the Paleo- 

 cene of either continent. 



I. Suborder Chelodactyla. Normal Perissodactyla. 



1. Equidce. Horses 



In order to make intelhgible the evolutionary changes which 



have led up to the modern horses, it will be necessary to say 



something concerning the dental and skeletal features which 



