2 74 Journal of Travel and Natural History 



the dentine of the Mastodon certainly seem less dense and fine 

 than that of the Elephant. With the view of throwing further 

 light on this point, Mr Waterhouse of the British Museum has 

 kindly caused a section to be made of a portion of the tooth of 

 the lower jaw of the Mastodon and of the tusk of the Deinothere. 

 Unfortunately the two teeth were not in an equal state of preser- 

 vation, which somewhat vitiates the result, but so far as it goes it 

 shews a closer and finer consistency in the Deinothere than in the 

 Mastodon. 



For these reasons, slight though they be, we are inclined to regard 

 the tusks of the Mastodon as being incisor No. i, the Elephant's 

 tusk being incisor No. 2. The temptation is great to regard the 

 tusks of the Deinothere as being incisor No. 3. 



The wish, perhaps, is father to the thought. It would complete 

 the series and harmonize with the succession propounded by Mr 

 Falconer for the other teeth of the three genera. It seems, too, 

 not unnatural that, when we find that the difference in the teeth 

 of two out of three of the forms of the same type makes its appear- 

 ance in different incisors, we should, when we find a third diffe- 

 rence in a third species, expect it to be manifested in another also. 



The most formidable objection seems to be that the symmetry of 

 the two jaws in the nine-tusker would require that the large teeth 

 in each should represent the same incisor in point of order. There 

 is, however, what appears to us a good answer to this. In the 

 Mastodon we know the tusks of the lower jaw are greatly smaller 

 than in the upper, and if this is to be accepted as a guiding rule, 

 it would follow that the Deinotheroid tusk in the lower jaw of the 

 nine-tusker is actually larger than the normal tusk in the upper 

 jaw, instead of being smaller, and, consequently, cannot represent 

 the same tooth. And this is one of the reasons for supposing it 

 to be incisor 3 — for the incisors, increasing in size gradually out- 

 wards, the largest should come last. And if we increase the 

 size of the Deinotheroid tooth in the same proportion that the 

 Mastodontoid tooth has to be, to give it the proportions of an 

 upper tusk, it would greatly exceed in size the Elephantoid tusk. 

 And the same remark applies to the Deinothere itself. At first 

 sight there would seem to be no means of comjxarison between the 

 tusks of the Elephant and those of the Deinothere, tlie one being 

 on the upper jaw, and the other in the lower. But if we take the 

 proportion of the size of the head into account, the proportion 

 between the lower and upper tusks of the Mastodon as a guide, 



