B. S. Lull — Evolution of the Elephant. 189 



the symphysis, and the lower tusks point directly forward 

 as in Mceritherium. The proboscis possibly did not extend 

 beyond the lower tusks while at rest, 

 though it could probably be extended be- 

 yond them. The premolar teeth have 

 two while the molars have three trans- 

 verse crests composed of distinct tubercles 

 and the cingulum of the hinclermost tooth 

 shows a strong tendency to form yet an- 

 other crest. There were twenty-six teeth FlG \ 15 ; To0 ^ of Pa- 

 altogether. The neck is still fairly long, 03omas ° on \ x i>- 

 though the hinder neck vertebrse are beginning to shorten. 



Ealcwmastodon is confined to the Upper Eocene, and has 

 thus far been found only in the Fay urn region. 



The Yale collection includes full-sized restorations of the 

 skulls of Mceritherium and Ealceomastodon as well as casts of 

 the type specimens, gifts of the British Museum of Natural 

 History. 



Classification of the Later Proboscidea. 



We know as yet no Oligocene proboscidians, the next forms 

 being found in the lower Miocene of northern Africa and 

 Europe, so that a considerable break occurs in the continuity 

 of our series. It is evident that the line was still African in 

 distribution, for apparently the exodus from Egypt did not 

 occur before Miocene times. 



The mastodons have been divided in two ways, one depend- 

 ing upon the number of ridges borne upon the grinders, while 

 the other classification is based upon the number and char- 

 acter of the tusks. The latter seems the more logical from a 

 developmental viewpoint. The first of these genera is Tetrabe- 

 lodon^ with four, enamel-banded tusks. The second is Eibelodon, 

 having but two tusks which still retain the band of enamel. 

 The last genus is Mammut, with enameless upper tusks in the 

 adult, though one or two may also be present in the adolescent 

 lower jaw. The latter are sometimes retained throughout life. 



Tetrabelodon. 



The third recorded stage in the evolution of the elephants is 

 represented by the Miocene Tetrabelodon angustidens, of 

 which a splendid specimen from Gers, France, is preserved in 

 the museum of the Jardin des Plantes at Paris. It was an 

 animal of considerable size, nearly as large as the Indian ele- 

 phant, but differing markedly from the latter in the peculiar 

 character of the lower jaw, which was enormously long at the 

 symphysis and contained a pair of relatively short tusks. This 

 form represents the culmination of the jaw elongation, for in 

 its successors the symphysis is rapidly shortened and the infe- 



