42 



bia River, but was replaced there by the American Elephant, 

 which preferred a milder climate. Remains of the latter have 

 been met with in Canada, throughout the United States, and in 

 Mexico. The last of the American Mastodons and Elephants 

 became extinct in the Post-Tertiary. 



The order Toxodontia includes two very peculiar genera, 

 Toxodon and Nesodon, which have been found in the Post-Ter- 

 tiary deposits of South America. These animals were of huge 

 size, and possessed such mixed characters that their affinities 

 are a matter of considerable doubt. They are thought to be 

 related to the Ungulates, Rodents, and Edentates, but as the 

 feet are unknown, this cannot at present be decided. 



Macrauchenia and Homalodoniotherium are two other peculiar 

 genera from South America, now extinct, the exact affinities 

 of which are uncertain. Anoplotherium and Palceolheriwn, so 

 abundant in Europe, have not been found in our North 

 American Tertiary deposits, although reported from South 

 America. 



Perhaps the most remarkable mammals yet found in Amer- 

 ica are the Tittodoniia, which are comparatively abundant in 

 the lower and middle Eocene. These animals seem to com- 

 bine the characters of several different groups, viz : the Car- 

 nivores, Ungulates, and Rodents. In the genus Tillotherium., 

 the type of the order, and of the family Tillotheridce, the skull 

 resembles that of the Bears ; the molar teeth are of the 

 ungulate type; while the large incisors are very similar to those 

 of Rodents. The skeleton resembles that of the Carnivores, 

 but the scaphoid and lunar bones are distinct, and there is a 

 third trochanter on the femur. The feet are plantigrade, and 

 each had five digits, all with long pointed claws. In the 

 allied genus Stylinodon, which belongs to a distinct family, the 

 Stylinodontidce, all the teeth were rootless. Some of these 

 animals were as large as a Tapir. The genus Dryplodon has 

 been found only in the Coryphodon beds of New Mexico, while 

 Tillotherium and Stylinodon occur in the middle Eocene of 

 Wyoming. Ancln'ppodus probably belongs to this group, which 



