OEDEES OF FISHES. 129 



able forms, of which one of the most singular is the Chfeto- 

 dont geuns Platax (fig. 498). 



Sub-order D. Plectognathi. — This sub-order is charac- 

 terised by the fact that the maxillary and premaxillary bones 



Fig. 49S. — Platax altissimus. A Cluetodnnt from the Eocene Tertiary of 

 Monte Bolca. 



are immovably connected on each side of the jaw. The 

 endoskeleton is only partially ossified, and the vertebral 

 column often remains permanently cartilaginous. The exo- 

 skeleton is in the form of ganoid plates, scales, or spines. 

 VOL. II. I 



