GREEN : ENCHODUS IN KANSAS MUSEUM. 79 



versed. Here the successional tooth appears behind the functional, which 

 is subsequently shed, and in old fish this tooth occupies a position be- 

 hind a concave symphysial portion which is edentulous, or only provided 

 with the small teeth of the marginal row. 



This description in its entirety applies only to the large 

 teeth of the dentary and pterygoid. And, moreover, the proc- 

 ess is not nearly so regular as one might suppose; but the 

 specimens would indicate that only one, or possibly two, teeth 

 on a dentary or pterygoid may be undergoing the process 

 of replacement at the same time. The teeth of Enchodus may 

 not properly be said to have roots, as they are anchylosed to 

 the bone. Also, it is found that many of the specimens which 

 show a tooth about to be replaced still have the base, and 

 sometimes the entire old tooth, standing immediately behind 

 the new tooth. However, granting that the process of re- 

 newal of the teeth takes place substantially in the manner 

 described, there arise several very interesting questions. 



Some of the palatines are found to have on their ventral 

 surfaces as many as fourteen scars of former fangs, and there 

 seems to be no good reason to suppose that the teeth on the 

 dentary and pterygoid are shed much less frequently. There 

 is ample proof that the dentary fang is not shed as often as 

 the palatine fang, yet it seems quite probable that all of the 

 teeth are renewed at about the same rate. Arising, as they 

 do, originally at nearly equidistant intervals, each of the teeth 

 on the pterygoid and dentary (except its fang) is superseded 

 by another which appears immediately in front of it; thus 

 it is very evident that, since the teeth migrate forward ap- 

 proximately by their own diameter at every succession, all 

 of the alveolar surface between the sites will soon have func- 

 tioned in the formation of teeth. Thus the fourth, or at most 

 the fifth, series will encroach on the territory previously 

 occupied by the fir.st set. - Could these old sites have functioned 

 a second time in the formation of teeth ? 



In case there were fourteen series of teeth on the dentary 

 during the life of the fish, and the teeth had arisen in the 

 first set at such intervals that there was room for three 

 teeth to stand between them, obviously the fourth series of 

 teeth would have to stand on the sites previously occupied by 

 the first set, except the most anterior one (not the dentary 

 fang as it migrates backward) , which would stand upon a new 



