198 H. SPENCllR HAREISON. 



early coucresceucej which by preventing separation at the 

 base materially interferes with any increase in size. There 

 are in all probability no successional teeth represented in 

 this portion of the jaw. The posterior uniform teeth we 

 have already considered, and a reference to the table on 

 page 194 will show the number present at various stages. I 

 believe that these teeth have never possessed a successional 

 set, and they have no vertical predecessors. 



Leaving out of account the uniform series, we are justified 

 in stating that there are at least three dentitions 

 represented in the functional teeth of the adult, 

 viz. a second and third in the persisting members of the 

 alternating series, and a fourth or fifth, or even some later 

 dentition, in the anterior teeth of both jaws. Perhaps 

 members of the later dentitions exist side by side in the 

 adult (as they do in the premaxilla of the young), and if so, 

 there may be four or more dentitions represented in the 

 adult. 



The vomerine teeth are undoubtedly in course of sup- 

 pression, as suggested by Howes (3). This is evident from 

 the infrequency of their occurrence (especially as paired 

 structures), and their small size in the adult when present: 

 this view is supported by the evidently degenerate condition 

 of one of the teeth in the specimen I have described. When 

 they occur they seem to begin their development about the 

 end of tiie incubation period, and I have found no indications 

 previous to Stage S. It is possible that they represent the 

 surviving members of two longitudinal series, as in two cases 

 one vomer has been found to possess two teeth, a smaller 

 one anterior to the larger ; there are also traces of an anterior 

 prolongation of the dental lamina on both sides in one of my 

 specimens. 



Contrary to the usually accepted statement, the teeth 

 of Hatteria have a well-developed outer coat of 

 enamel. I have seen this in its earliest stages of develop- 

 ment, and I give a figure of a portion of the fully formed 

 tooth, showing the dentinal tubules branching near their 



