DEVELOPMEIST OF TEETH IN HATTERIA PUNCTATA. 203 



of the second and third dentitions by one of the fourth 

 dentition. In my oldest specimen the fourth is the 

 functional dentition in the premaxilla, though there is one 

 of the fifth on the point of displacing its predecessor of the 

 fourth. It is quite possible that more successional teeth 

 will be found in this region on examination of later stages.^ 

 Each adult "incisor" tooth has two components, 

 but the union is not due to concrescence, being caused 

 by intimate fusion with the bone, which embraces the bases 

 of the teeth and also grows down beyond the gums, thus 

 increasing the apparent size of the compound tooth. Hatteria 

 does not foreshadow the heterodont condition of higher 

 types, but is truly homodont. 



6. In the maxillae the anterior alternating teeth are sub- 

 ject to replacement by members of the fourth dentition, each 

 of these replacing, in some cases at least, two of the alter- 

 nating series. I have found one successional tooth which I 

 believe to represent the fifth dentition in the maxilla. The 

 first four teeth of the adult maxilla are usually successional 

 (i. e. belong to the fourth or a later dentition). 



7. The only successional tooth I have found in the pala- 

 tines was situated lingually to No. 2 (second dentition). It 

 replaces in all probability both Nos. 1 and 2, and may be seen 

 in many adult specimens as a large tooth at the commence- 

 ment of the palatine series, if, indeed, this does not represent 

 a still later dentition, e. g. fifth or sixth. 



8. The vomerine teeth are in course of suppression. They 

 may be paired or unpaired, and one may show signs of 

 degeneration in structure. In some cases two teeth have been 

 found on one side. In most specimens they are completely 

 absent, probably during the whole of development. The 

 dental lamina is not a conspicuous structure, but appears to 

 have a short prolongation anterior to the teeth. We are 

 perhaps here dealing with the surviving members of two 

 longitudinal series. 



9. The anterior portion of the mandible at one stage 



' See Addendum. 



