GANOIDEI. 319 



fishes. The endoskeleton is only partially converted into bone, 

 and the exoskeleton, by way of compensation, consists of 

 ganoid plates. The swim-bladder is destitute of an air-duct. 



This sub-order comprises the living Pipe-fishes (Syngna- 

 thidce) and Sea-horses (Hippocampidce). A few fossil forms are 

 known, dating from the Eocene Tertiary. 



Fig. 281. Platax altissimus, a Chsetodont from the Eocene Tertiary of Monte Bolca. 



ORDER II. GANOIDEI. The order of the true Ganoid 

 Fishes may be defined by the following characters. The endo- 



