O. C. Marsh— Vertebrate Life in America. 865 
been supposed, — very recently, that our Eocene contained 
no eyen-hoofed mammals. 
n the lowest Macéens of the West, no re crescent-toothed 
Artiodactyla have as yet been identified, the exception 
of a single species of Hyopotamus ; but in a overlying beds 
of the middle Miocene, remains of the Oreodontide occur in 
such vast numbers as to indicate that these animals must 
have lived in large herds around the borders of the lake-basins 
in which their remains have been entombed. These basins are 
now the denuded deserts so well termed Mauvaises Terres by 
the early French trappers. The least upecialineds and apparently 
the oldest, genus of this group is Agriocherus, which so nearly 
resembles the older H: yopotamus, and the stil] more ancient 
fomeryx, that we can hardly doubt that they all belonged to 
the same ancestral line. The typical Oreodonts are the genera 
In the nthe Pliocene formation, on each side of the 
Rocky Mountains, the genus wire a = one of the ath 
forms, and continues the line on he Miocene, where 
oe) r surviving until the Post- are, so far as know 
A tibet interesting line, that leading to the Camels and ee 
mas, separates from the primitive Selenodont branch in the 
Hocene, probably through the genus Parameryx. In the Mio- 
ene, n Pebrotherium and some nearly allied forms 
ine ataeabie ‘ndibationh that the Cameloid type of ruminant 
had already become partially specialized, although there is a 
complete series of incisor teeth, and the metapodial ogee are 
distinct. In the Pliocene, the ‘Camel tribe was, next the 
Horses, the most vetoes of the = mammals, The Tine j is 
e home of vast numbers e Camelide, and there can be 
little doubt that they eousee here, and migrated to the Old 
World. 
