HISTORY OF THE ARTIODACTYLA 361 



whence the other was derived, and many transitional forms 

 are known. 



The classification of the immense horde of hving and extinct 

 genera and species which are referable to the artiodactyls 

 is an extremely difficult problem, which has found no thoroughly 

 satisfactory solution and will not until much more is learned 

 concerning the history of the order and conflicting opinions 

 can be reconciled. The most important American families 

 and genera are given below, though the arrangement is but 

 tentative. 



Suborder A. ARTIODACTYLA fPRIMITIVA. (Extinct genera of 



doubtful affinities) 



I. fTRIGONOLESTID^. 



^Trigonolestes, low. Eoc. 



II. fLEPTOCHCERID.E. 



fLeptochcerus, low. Oligo. fStibai'Us, low. Oligo. 



III. fDiCHOBUNiD^. ^Homacodon, mid. Eoc. \Bunomeryx, up. Eoc. 



IV. fANTHRACOTHERIIDiE. 



^ Anthracotherium, low. Oligo. \ Bothriodon, do. \Arretotherium, 

 do. 



V. ? fOREODONTID^. 



'\ Protoreodon, up. Eoc. \Merycoidodon, low. Oligo. '\Eporeodon, 

 up. Oligo. \ Promerycochoerus, up. Oligo. to up. Mioc. ]Mery- 

 cochcerus, Mioc. and low. Plioc. '\ Pronomotherium, up. Mioc. 

 "fMesoreodon, low. Mioc. fMerychyus, low. Mioc. to low. Plioc. 

 ^Leptauchenia, low. Oligo. to low. Mioc. ]Cydopidius, mid. 

 Mioc. 



VI. fAGRIOCHCERID^. 



\Protagriochcerm, up. Eoc. \ Agriochcerus, Oligo. 



Suborder B. SUINA. Swine-like Animals 



VII. Tagassuid^Ej Peccaries. 



^Helohyus, mid. Eoc. ^Perchoerus, low. Oligo. ^Thinohyus, up. 

 Oligo. \Desmathyus, low. Mioc. ^Prosthennops, up. Mioc. and 

 low. Plioc. ]Platygonus, mid. Plioc. to Pleist. Tagassu, Recent, 

 Pleist. in S. A. 



VIII. fENTELODONTID.E. fGriant PigS. 



^Parahyus, low. Eoc. ^Achoenodon, mid. and up. Eoc. ^Archceothe- 

 rium, low. Oligo. ^Boochoerus, up. Oligo. ^Dinohyus, low Mioc. 



