612 UNGULATES. 



sition that the Dinotherium had a seventh molar or fourth true 

 molar, to which Kaup originally referred the comparatively small 

 and simple tooth which he has figured in his * Ossemens Fossiles 

 de Darmstadt', PI. ii, figs. 7, a, b ^ c, and which I regard as 

 being more probably the first deciduous molar of the lower jaw. 



As the Tapir recedes from the Palaeothere by the non-de- 

 velopment of the tooth answering to the first lower premolar, so 

 the Dinothere recedes from the Tapir in the non-development of 

 the teeth answering to the first and second premolars in both 

 jaws. And as the Lophiodon manifested a more simple form of 

 the posterior premolars than in the existing Tapir, so also, the 

 Dinothere manifested a still more simple form of the tooth cor- 

 responding to the second lower premolar in Lophiodon, and to 

 the third in the False othere. By the third ridge of the last 

 deciduous molar, the Dinothere manifested in this transitional 

 dentition a character which is retained in the permanent dentition 

 of the Lophiodon. 



The generic peculiarity of the Dinotherium is most strongly 

 manifested in its tusks. These tusks (PI. 96, fig. 6) are two in 

 number, implanted in the prolonged and deflected symphysis of 

 the lower jaw, in close contiguity with each other, and having 

 their exserted crown directed downwards and bent backwards, 

 gradually decreasing to the pointed extremity : each tusk has a 

 slight longitudinal depression on its outer side : the long implanted 

 base is excavated by a wide and deep conical pulp-cavity, like the 

 tusks of the Mastodon and Elephant. In jaws with molar teeth of 

 equal size the symphysis and its tusks offer two sizes : the larger 

 ones, which have been found four feet in length with tusks of two 

 feet, may be attributed to the male Dinotheres, the smaller specimens 

 with tusks of half the size, to the females. The ivory of these tusks 

 presents the fine concentric structure of those of the Hippopo- 

 tamus, not the decussating curvilinear character which characterises 

 the ivory of the Elephant and Mastodon. No corresponding tusks, 

 nor the germs of such, have yet been discovered in the upper 

 jaw of the Dinotherium. 



It is highly probable from the shape of the skull of the 



