LEIODON. 261 



The necessity under which Cuvier felt himself compelled to 

 regard the crown and the base of the tooth of the Mosasaur as two 

 distinct parts, is at once banished by the recognition of the principle, 

 that the processes of calcification are essentially the same at every 

 part of a tooth, whether it be free or anchylosed ; and that they are 

 modified only, as I have shown in my Memoir on the formation of 

 the teeth of the shark, (1) according to the density of the part to be 

 produced. 



107. Leiodon. — In the English chalk-formations a few vertebrae 

 have been found which are generically, if not specifically related to the 

 Maestricht Mosasaur ; but as yet the only teeth which approach in 

 form to those of this genus are those from the Norfolk- chalk alluded to 

 by Dr. Mantell in his " Wonders of Geology," (vol. 1, p. 339) as 

 belonging to an unknown reptile or to a sauroid fish. The portion of 

 the jaw to which they were attached exhibits the mode of attachment 

 of the teeth, which so closely corresponds with that of the Mosasaur 

 as to leave scarcely any doubt of their near relationship : it is by no 

 means improbable that this fragment of jaw and teeth may belong to 

 the same species as the vertebree above alluded to ; for these essential 

 parts of the organization would retain their generic characters little 

 if at all altered in a species of Mosasaurus that might be distin- 

 guished from the Maestricht fossil and be characterized by well 

 marked modifications of the form of the teeth. Until, however, 

 this conjecture be refuted or confirmed, the reptile, to which the teeth 

 in question belonged, may be indicated by the name of Leiodon(2), in 

 reference to the smooth and polished surface of the teeth. The fossil 

 to which the foregoing observations refer is figured, of the natural 



s'ossifiant aussi et en s'unissant, et a I'os maxillaire et au noyau devenu osseux, enchasse et sertit 

 la dent avec une nouvelle force." Cuvier proceeds to remark, " On congoit tres bien que ce noyau, 

 identifie avec I'os maxillaire puisse, subir les memes changemens que lui ; que I'alveole de la dent 

 de remplacement puisse penetrer sa solidite ; que la compression puisse le detacher, soit en le cas- 

 sant, scit en obliterant les vaisseaux qui le nourrissent ; en un mot, qu'il soit expose a des revolu- 

 tions analogues, comme je I'ai dit, a celle du bois des cerfs, mais tres difFerentes de celles qu'e- 

 prouve la dent qui est toujours un corps devenu etranger a ranimal qui I'a secrete, ainsi que je 

 I'ai demontre, apres Hunter, dans mon chapitre sur les ossemens d'elephans."— Ossem. foss. 

 Ed. 1836, vol. X. p. 136. 



(1) Comptes Rendus, Dec. 16, 1839. 



(2) Xiiog, smooth; oSuq, a tooth. 



