178 



THE STORY OF FISH LIFE. 



preserved to us, take the form of very large and 

 thick overlapping scales, coated externally with 

 an enamel-like substance known as "ganoine" 



FIG. 15. A. Restoration of a primitive Sturgeon Cheirolepis, after 

 Traquair. B. The African "bichir," Polypterus bichir, living 

 in the Nile at the present day. Note the heavy armour of rhom- 

 boid scales. C. Restoration of the extinct lung-fish, Holoptychius, 

 after Traquair. 



(hence the old name " ganoid " fishes). In addi- 

 tion these scales were also more or less elaborately 

 sculptured. The head was encased in hard, 

 closely-fitting plates. 



Other forms of this period have rhomboid 



