1903.] Hay, North American Cretaceous Fishes. 67 



palatine as a mass of osteodentine ; but to the present writer 

 this mass, as also that composing the tritoral plates of Anog- 

 mius, appears to be merely very compact bone. 



Dr. Loomis has probably given us the correct explanation 

 of the replacement of the palatine fangs. The new fang is 

 produced in front of the senescent one. Originally the latter 

 had stood on the very anterior extremity of the palatine 

 bone, but after the tooth had become affixed, the bone 

 prolonged itself in front of the base of the tooth and thus 

 provided a surface for the attachment of the next fang in 

 succession. When the new tooth has taken its position, its 

 predecessor, through absorption of its base, is loosened and 

 drops away, leaving a crescentic scar. Sometimes several of 

 these scars may be observed on the palatine. The new tooth 

 probably became firmly fixed before its predecessors fell 

 away; otherwise it would have been easily wrenched from 

 its moorings. It will probably also be found that there is 

 an alternation in the replacement of the fangs. Evidence of 

 this is found in the palatines of No. 2098. The right palatine 

 has a conspicuous process of bone extending forward over 

 the base of the fang. The left palatine has only the slightest 

 trace of such a process. 



The large teeth on the anterior end of the pterygoid are 

 replaced also by the development of others in front of them ; 

 and the scars resulting from the falling away of the old teeth 

 may be seen. On the other hand, the great fang on the 

 anterior end of the dentary is replaced by the growth of 

 another behind it, and the scars of former teeth lie in front 

 of the functional fang. Prof. Cope's figure (Vert. Cret. Form. 

 West, pi. liv, fig. 3) shows the end of the right dentary from 

 without. The functional fang is broken off some distance 

 above its base. In front of it is an elevation of bone on 

 which stood the replaced fang. In the specimen, the surface 

 of the scar looks as if the old fang had only recently been 

 broken off. Cope's figure ^a is unsatisfactory. Other speci- 

 mens of Enchodus confirm the conclusion that the new fang of 

 the dentary is produced behind the old one. Thus, while the 

 fang of the palatine is moving forward, that of the dentary is 



