green: ENCHODUS in KANSAS MUSEUM. 81 



that the teeth on the dentary and pterygoid are likewise re- 

 placed early in the life of the fish, although no small scars are 

 left as evidence of the fact, as is the case with the palatine. 

 These facts would indicate that the large teeth of the mandibles 

 (excluding the fangs) do migrate cephalad past the original 

 sites of the first series of teeth, and that the scars left by the 

 earlier teeth are obliterated in the process. This is probably 

 accomplished by a migration cephalad of the odontoblasts and 

 enamel cells into the scar areas of the completely absorbed 

 bases, these two classes of cells always remaining grouped in 

 the neighborhood of the bases of the functioning teeth. Quite 

 often the new teeth are inclined cephalad at their bases, due, 

 presumably, to the presence of the old base. (PI. II, fig. 2, d.) 

 Since the extent of individual variation has not yet been de- 

 termined, no satisfactory key to the species can be off'ered at 

 present, but it is hoped that the following may prove helpful. 

 To which group Enchodus fcrox belongs can not be determined ; 

 but because of its large size, it is very probable that it should 

 be placed in the group with EnchodiiR petrostis, although 

 whether it has the row of minute teeth on the external alveolar 

 border of the dentary or not is not known, this species being 

 based upon a single palatine. 



Having no marginal fringe of minute teeth on the external, alveolar 

 border of the dentary: 



Petrosns group. 

 Palatine fang not situated at the cephalic end of the palatine, but having 

 the palatine projecting forward from the base of the fang more than 

 one-fifth as far as it extends behind it; size as large or larger than 



E. pctrosus Enchodus ferox 



Palatine fang not laterally compressed ; an elongate foramen near the 

 mesial border of the premaxillaries; length of palatine fang, 30 to 



40 mm Enchodus petrosns 



Palatine fang laterally compressed; cutting edge in front only; pre- 

 maxillaries not as above r a smaller species; length of the palatine 



fang, 15 to 20 mm Enchodus diru<; 



Palatine fang straight and relatively slender; distinctly fluted mesio- 

 caudally; palatine with relatively great vertical thickness; no fora- 

 men in the premaxillaries; the smallest species in this group; length 

 of the palatine fang 15 to 18 mm Enchodus amicrodus 



