102 MESSRS. HANCOCK AND ATTHEY ON 



reconnait au plus fort du renflement exterieur une ligne circulaire 

 qui indique la limite du capuchon emaille et de la dentine. La 

 dentine elle-meme n'offre rein de remarquable. Les tubes cal- 



ciferes Ceux du sommet se continuant, comme 



chez le Polypterus, dans 1' email, ou ils paraissent plus roides, 

 mais en meme temps plus fins et moins regulierement disposes 

 que dans le dentine." 



Of PolyjJterus the same author writes as follows : — " Cette 

 dentine forme la plus grande partie de la dent ; elle n'est recou- 

 verte qu'au sommet par un petit capuchon d'email tresdur, et 

 dans lequel je n'ai pu reconnaitre ces fibres composees de petits 

 cubes superposes, telles qu'on les a reconnues chez les mammi- 

 feres. L' email du Polypterus (fig. 12) est transparent comme du 

 cristal, sans trace de structure, et ce n'est que dans sa base que 

 penetrent les dernieres extremites effilees des canaux calciferes 

 de la dentine," etc. 



Respecting Saurichthys it is stated : — " Cette difference entre 

 le socle et le sommet est encore plus frappante, lorsqu'on exa- 

 mine leur structure au microscope ; le premier est compose de 

 dentine, le dernier d'email. La cavite pulpaire est un cone creux 

 entoure d'un cone de dentine massive, sur lequel repose le ca- 

 puchon emaille comme dans les dents du Polyptere." This de- 

 scription of the structure of the tooth of Saurichthys is very 

 different from that given in the " Odontography," p. 170, where 

 the cap of enamel is certainly described, but not recognized as 

 such ; the author apparently not being aware of the difference 

 between the base and the summit, pointed out by M. Agassiz. 

 And, indeed, the description seems to be confined to the ena- 

 melled or upper portion alone, the basal portion evidently, having 

 been deficient in the specimen examined. 



Similar passages might be quoted repecting Lepidosteus ; but 

 perhaps enough has been said on the supposed recent discovery 

 of the " emamel-tipped spear teeth." We have seen that M. 

 Agassiz fully described and accurately figured this form of tooth 

 in four genera (Plate III., figs. 3, 4) between twenty and thirty 

 years ago (1833-1844) ; and we have determined its existence 

 in four other genera, and have likewise verified the accuracy of 



