338 



PALEOZOIC SYSTEM OF KOCKS. 



Of the Placoids we can not give figures of the forms, as these are not 

 known ; but their teeth and enormous spines are found (Figs. 435, 436). 



Classification of Devonian Ganoids. — As above described, Devonian 

 Ganoids fall naturally into two groups — viz., Lepido-ganoids (scale 



Figs. 437^42.— Nearest Living Allies of Devonian Fishes: 437. Lepidosiren. 438. Ceratodus 

 Fosterii, x ■& (after Gunther). 439. Polypterus. 440. Lepidosteus (Gar-Fish). 441. Amia 

 (American Mud-fish). 442. Cestracion Phillippi (a Living Cestraciont from Australia). 



