686 THE POPULAR SCIENCE MONTHLY. 



Ungulates as a distinct order, make their first appearance in North 

 America in the lower Pliocene, where several species of Mastodon 

 have been found. This genus occurs, also, in the upper Pliocene, and 

 in the Post-Tertiary ; although some of the remains attributed to the 

 latter are undoubtedly older. The Pliocene species all have a band 

 of enamel on the tusks, and some other peculiarities observed in the 

 oldest mastodons of Europe, which are from essentially the same hori- 

 zon. Two species of this genus have been found in South America, in 

 connection with the remains of extinct llamas and horses. The <renus 

 Elephas is a later form, and has not yet been identified in this country 

 below the upper Pliocene, where one gigantic species was abundant. 

 In the Post-Pliocene, remains of this genus are numerous. The hairy 

 mammoth of the Old World {Elephas primigenius) was once abundant 

 in Alaska, and great numbers of its bones are now preserved in the 

 frozen cliffs of that region. This species does not appear to have 

 extended east of the Rocky Mountains, or south of the Columbia 

 River, but was replaced there by the American elephant, which pre- 

 ferred 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 JVesodon, which have been found in the Post-Tertiary 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 Ilomalodontotherium are two other peculiar 

 genera from South America, now extinct, the exact affinities of which 

 are uncertain. Anoplotherium and Palwotherixmi, 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 America are 

 the Tillodontia, which are comparatively abundant in the lower and 

 middle Eocene. These animals seem to combine the characters of 

 several different groups, viz., the Carnivores, 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 trochan- 

 ter 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 Stylinodontidw, all the teeth were 

 rootless. Some of these animals were as large as a tapir. The genus 



