THE 



SIXTH ORDER OF FISHES. 



THE PLECTOGNATHI, 



May be approximated to the chondropterygii, to 

 which they are allied a little in the imperfection of the 

 jaws, and in the slowness with which their skeleton 

 hardens; nevertheless, this skeleton is fibrous, and 

 its entire general structure is that of ordinary fishes. 

 Their principal distinctive character consists in the 

 maxillary bone being soldered or fixedly attached on 

 the side of the intermaxillary, which alone forms the 

 jaw, and to which the palatine arch is dovetailed by a 

 suture with the cranium, and consequently has no 

 power of motion. The opercula, moreover, and the 

 rays, are concealed under a thick skin, which only per- 

 mits a small branchial cleft to be visible externally l . 



1 This disposition, the commencement of which is already observ- 

 able in the chironectes, has caused many naturalists to believe that 

 the plectognathi wanted opercula and rays : they possess them like 

 other fishes. 



O O 2 



