374 PHILOSOPHY OF ZOOLOGY. 



The most convenient distribution of fishes which has yet 

 been proposed, is that which depends on the conditions of 

 the osseous system. In one division, denominated Carti- 

 laginous, the bones are soft, and destitute of fibres ; while 

 in the other, termed Osseous, the bones are more soUd, and 

 of a fibrous structure. 



ORDER. I. 



Cartilaginous Fishes. 

 In this group, the cartilaginous basis seems to prevail, 

 and the calcareous matter is never distributed in percepti- 

 ble filaments. The cranium forms only one connected 

 plate destitute of sutures, and all the articulations of the 

 different parts of the skeleton are indistinct. The maxil- 

 lary and intermaxillary bones are wanting or imperfect, 

 and their place is supplied by a development of the pala- 

 tine bones and vomer. 



1st Subdivision. 



Chondropterygious Fishes. 



Branchiae fixed. 



1st Tribe. 



Lips fitted to act as a sucker. 



The skeleton of the fishes of this tribe, is very imper- 

 fectly developed. The lips are strengthened by a cartila^ 

 ginous ring. The branchiae are placed on the walls of len- 

 ticular cavities. The labyrinth of the ear is in the interior 

 of the cranium. The nostrils open by one aperture. 



A. Seven branchial apertures on each side, and the same 

 number of cavities. 



(1.) Maxillary ring armed with teeth. 



1. Petromvzon. Lamprey. Margin of the mouth 

 destitute of a beard. P. marinus and Jluviatilis. 



2. HoMEA. Maroin of the mouth bearded. 



