SALMONOIDS. 141 



become more regular and parallel. This parallelism has taken place 

 in the Phyllodus, much sooner in the dentine than in the enamel, 

 as is the case in the Scarus, and hence the difference of the disposi- 

 tion of the fine calcigerous tubes, which mainly distinguishes the 

 texture of the dentine and enamel in fishes. 



The fossils here described very clearly exhibit the effects of 

 attrition and waste at one extremity, and of renovation at the 

 opposite end of the dental mass ; but they likewise show the 

 same antagonist influences operating at the upper and the lower 

 surfaces of the mass ; the work of destruction and of reproduc- 

 tion has proceeded in both the longitudinal and vertical 

 directions. As the lamelliform teeth at the top of each pile were 

 worn away, the loss was supplied by new lamellae added to the bottom 

 of the pile, according to the mode of reproduction described in the 

 dental system of the Diodon. But as the attrition was greatest at 

 the anterior extremity of the dental plate, and the power of repro- 

 ducing the lamellae in the vertical direction limited, the loss of 

 entire piles of teeth was supplied by the addition of new piles to the 

 posterior extremity of the dentigerous plate, according to the mode 

 of reproduction described in the pharyngeal teeth of the Scarus. In 

 the Diodon we see illustrated the law of succession of the permanent 

 to the deciduous teeth in the Mammalia, viz: in the vertical direction, 

 but the process is much more frequently repeated. In the Scarus, the 

 course of succession of the true molars in the Mammalia, viz : in the 

 horizontal course was followed. In the Phyllodus, both kinds 

 of displacement and succession are exemplified ; and the peculiarities 

 of the Diodon and Scarus were combined, with the same frequent and 

 uninterrupted repetition of the renovating processes, in a single 

 dentigerous bone of that extinct species. 



SALMONOIDS. 



57. Many fishes of the Salmon tribe, like those of the Clupeoid 

 family, have the superior margin of the mouth formed in a greater or 

 less degree by the superior maxillary as well as by the intermaxillary 

 bones, both of which, excepting in the edentulous species, as the 

 Salmo edentulus,{\) Bloch, are armed with teeth. 



(1) The type of the genus Anodus of Spix. 



