THE ARCTOG^IC REALM. [CHAP. 



lower Pliocene of India, while species also occur in the Miocene of 

 the United States, has molars strikingly like those of the Titano- 

 theriida, but its feet differ from those of all existing ungulates in 

 terminating in huge curved claws much resembling those of 

 the South American edentates. Indeed, one genus of the family 

 (Macrotheriuni] was long regarded as belonging to the latter 

 group. Of the two genera which occur in the European Miocene, 

 Macrotherium has the fore limb much longer than the hinder ; 

 whereas in Chalicotherium (Ancylotherium) the two are more nearly 

 equal in length. It is to the former genus that the North American 

 forms are assigned. 



The proboscidean ungulates, which differ markedly from the 

 two preceding groups in the structure both of their teeth and 

 limbs, and are now represented only by the Indian and African 

 elephant, form a comparatively small assemblage, most of whose 

 members may be included in the family Elephantida. Among 

 these, the most specialised types constitute the genus Elephas, 

 characterised by the complexity of the structure of the cheek-teeth, 

 which generally assume the form of more or less elevated parallel 

 plates, with the intervals filled with cement. In certain of the 

 earlier species from the Pliocene of Asia the plates of these teeth 

 are, however, comparatively low and less numerous, with the 

 intervening valleys almost devoid of cement; so that these 

 stegodont elephants, as they are called, form a complete transition 

 towards the mastodons. Commencing in the Indian Pliocene, 

 elephants ranged over the whole of Europe and Asia during the 

 Plistocene, while we have also evidence of their occurrence during 

 the same epoch in northern Africa; and they were likewise repre- 

 sented by two species in North America, one of which ranged as far 

 south as Texas. One of these American species was identical 

 with the European mammoth (E. primigenius], while the second 

 (E. columbianus] was nearly allied; both being near relatives of the 

 existing Indian elephant. The extinct stegodont elephants being 

 confined to south-eastern Asia, it is interesting to note that the 

 species of Mastodon making the nearest approximation to Elephas 

 are met with in this region alone; and from this it may be inferred 

 that the evolution of the latter genus took place in that part of* the 

 world. All mastodons, it may be mentioned, have comparatively 



