THE MASTODONS 1143 



an exceedingly interesting group, which almost completely connects the true ele- 

 phants with the under-mentioned mastodons. A molar tooth of one of the species of 

 this group is represented on p. 1115; this tooth, as already mentioned, 



being characterized by the small number of its ridges (in this instance 

 Elephants 



six), which are very low and wide, with the shallow intervening 



valleys devoid of cement. In other species of the group the ridges were, however, 

 somewhat more numerous and more elevated, while the valleys were partially rilled 

 with cement; and these serve to connect the figured Cliffs elephant with species 

 like the southern elephant. It will be observed that the tooth of Cliffs elephant, 

 represented on p. 1115, agrees with existing species in having the transverse ridges 

 undivided by any distinct longitudinal cleft. One of the stegodont elephants (E. 

 ganesa) is remarkable for the enormous size of its tusks, those in a skull from the 

 Siwalik hills, preserved in the British Museum, measuring upward of twelve feet 

 nine inches in length, with a maximum girth of twenty-six inches. Representa- 

 tives of this group also occur in China, Japan, and Java. 



THE MASTODONS 

 Genus Mastodon 



The above-mentioned stegodont elephants so closely connect the genus Elephas 

 with the extinct animals known as the mastodons, that the division between the 

 two genera is a somewhat arbitrary one. It is noteworthy that the species of mas- 

 todons most nearly related to the stegodont elephants are found in the same regions 

 as the latter, from which me may infer that the evolution of the elephants from the 

 mastodons took place in Southeastern Asia. 



Mastodons are distinguished by their molar teeth, as shown in the figure on the 

 next page and the one on p. 1145, having comparatively-few transverse ridges, which 

 are low, and more or less completely divided by a longitudinal cleft into inner and 

 outer columns. These ridges are separated by valleys in which there is little or no 

 cement; and when worn down by use they exhibit more or less trefoil-shaped sur- 

 faces of ivory, quite different from the elongated ellipses formed in those of the true 

 elephants. In the third, fourth, and fifth molar teeth of the stegodont elephants, 

 the number of transverse ridges is usually more than six, but in the mastodons it is 

 generally either four (as shown in the cut on p. 1 144) or three, although occasionally 

 there may be as many as five. Moreover, the sixth or last molar generally has only 

 four or five such ridges, in place of from nine to eleven found in the stegodont ele- 

 phants. In all these respects the mastodons exhibit a less specialized type of struc- 

 ture than that existing in the elephants, and thereby approximate to ordinary 

 Ungulates. This simpler dental structure is further evidenced by the circumstance 

 that portions of three molar teeth may be in use at the same time, whereas in ele- 

 phants only two such teeth are ever present contemporaneously on one side of the 

 jaw. Then, again, nearly all the mastodons had premolar teeth vertically replacing 

 their milk-molars, in the same manner as in other Ungulates. 



