ELEPHANT AND MASTODON. 41 



these instances, is greater than between the corresponding upper 

 molars of the two species. This specimen measures 7.2 inches 

 in leno-th. 



o 



If the eye is carried along these sections in succession, it will 

 be readily perceived that they constitute a series of gradations in 

 form conducted from E. insignis to E. Africanus, through E. 

 planifrons. The modifications are effected by the elongation and 

 thinning of the ridge-plates, with a corresponding increase in the 

 depth of the hollows, and in the vertical height of the teeth ; by 

 a diminution of the basal mass of ivory ; by a greater number of 

 divisions in the same extent of tooth surface, and a gradual dimi- 

 nution in the thickness of the layer of enamel. Plate 1, repre- 

 sents another succession of links which, in like manner, conduct 

 us from the African Elephant on to the extremity of the series 

 in E. primigenius. 



Fig. 3 a, of this plate shows a section of the penultimate upper 

 molar of an undescribed Indian fossil species named E. Hysu- 

 dricus in this work. The tooth is in the middle stage of wear, 

 eleven of the thirteen plates of which it is composed, having been 

 in use, and the two anterior ridges being worn out. The same ver- 

 tical disposition of ivory, enamel, and cement, is presented as in the 

 African Elephant, but the plates are thinner and a greater num- 

 ber of them is included in the same length, nine or ten plates 

 in the latter being developed in the space occupied by thirteen 

 or fourteen plates in the equivalent teeth of E. Hysudricus. The 

 plates are also more vertical, the interspaces occupied by the 

 cement are wider in general than the ivory plates which represent 

 very attenuated wedges. The layer of enamel is proportionally 

 thicker than in the African Elephant, approaching, in this respect, 

 the teeth of E. planifrons, fig. 5. The vertical height of the tooth 

 is comparatively less in this specimen than in the African species, 

 the difference being compensated by a greater development of 

 the basal mass of ivory. This specimen measures 7-7 inches in 

 length. 



A portion of the last molar of the lower jaw of this species is 

 shown in vertical section in fig. 3 b, comprising about fifteen 



