CLUPEOIDS. 135 



~th of an inch in diameter, in which I could perceive neither 

 branches, anastomoses nor cells. The exterior ivory-like substance 

 viewed in a section of a Pike's tooth by a low magnifying power resem- 

 bles a layer of enamel. It is extremely thin where it commences 

 near the base of the tooth, and is thicker at the apex where the fine 

 branches of the tubes exhibit the most beautiful dendritic arrange- 

 ment. The central substance of the tooth is grey in recent teeth, 

 and yellowish in dried specimens ; the peripheral substance is of the 

 purest white, and is much harder and more compact than the central 

 substance. So hard, indeed, is it in dried teeth, that I supposed it 

 might be covered with an extremely thin layer of enamel, but I could 

 not by means of the microscope discover any such layer." 



CLUPEOIDS. 



54. The Clupeoid family of Fishes, of which the Herring is the 

 type, is interesting in relation to the dental anatomy of the class on 

 account of the examples which it offers of very general and extensive 

 distribution of teeth over the bones which surround the oral cavity, 

 and of the unusual share which the superior maxillary bones, from 

 their relative position and development, take in supporting the 

 teeth of the upper jaw. The different genera, however, of the 

 Clupeoid, as of other natural groups of fishes, present very diver- 

 sified conditions of the dental system ; the almost edentulous Clupano- 

 don, and the rapacious Erythrinus or the gigantic Sudis, offering the 

 extremes of these modifications. 



In the Clupanodon an almost imperceptible coating of the finest 

 villiform teeth, upon the pharyngeal bones, forms the sole trace of a 

 dental system.. 



The Herring {Clupea Harengus) has very minute sharp-pointed 

 teeth on the jaws and tongue. 



The Pristigaster presents similar teeth on the large intermaxilla- 

 ries, on a small part of the superior maxillaries, and upon the hyoid, 

 palatine, vomerine and pterygoid bones. 



The Httle Anchovy, the type of the genus Engraulis, is a good 

 example of that higher development and allocation of the superior 

 maxillary bones, which is so rare in the class of fishes ; they here 



