258 O. C. Marsh—Notice of New Tertiary Mammals. 
and also the characteristic astragalus, with its pig oe 
superior ridges, and its small articular facet for the ¢ 
= do 
| Ba 
ert 
“< 
changes that seem to have produced in America the hi 
specialized modern Hguus from his diminutive, four-toed prede- 
cessor, the Eocene Orohippus. The line of desvent appears to 
have been direct, and the remains now known supply every 
important intermediate form. It is, of course, impossible to 
with certainty through which of the three-toed genera of 
ths Pliocene that lived together, the succession came. It is not 
impossible that the later species, which appear generically iden- 
tical, are the descendants of more distinct Pliocene t as 
Yale College, New teak Feb, 20th, 1874, 
