194 



H. SPENCER HARRISON. 



between the dentition of the last specimen described and that 

 of the adult. 



The great majority of adult Sphenodons show two large 

 "cusps" to each incisor. In some cases there are in addi- 

 tion one or two minute projections, which have sometimes 

 been taken for cusps. I believe, however, that these are 

 merely portions of an overgrowth of bone that occurs round 

 the base of many of the adult teeth. It appears certain that 

 there are only two teeth concerned in the formation of each 

 adult premaxillary tooth, Knox (21), it is true, stated that 

 he found a specimen with three cones to each, but his de- 

 scription is very brief and not at all clear. I have shown 

 that in my largest young animal the third successional tooth 

 is on the point of replacing the first. All the three teeth of 

 the newly-hatched animal are lost. In the absence of other 

 young specimens I prefer to reserve judgment as to whether 

 the two main teeth of my specimen (i. e. the second and third 

 successional, see figs. 21, 22) are the two components of the 

 adult tooth. On the whole, I think it is very probable that 

 there may be a constant succession of teeth in this region 



1 If the two successional teeth have each replaced two of the alternating 

 series, 16 would be the correct number. All the figures given are approxi- 

 mate, as sometimes the two sides differ sh'glitly. (See also Addendum.) 



