122 THE CHAIN OF LIFE. 



The head-shield copied in outline in Fig. 104, and the restora- 

 tion after Lankester in the frontispiece to this chapter, may 

 serve to represent these curious primitive Ganoids, which are 

 continued in the Devonian fishes represented in Figs. 105, 106. 

 Along with these, and not improbably their enemies, were 

 certain Sharks (Fig. 104), known to us only by the spines which 



Fig. xo^.—Cephalasph Z?a«/Jo«« (Lankester). Lower Devonian of Gaspd. 



were attached to their fins as weapons of defence, and by 

 detached bony tubercles which protected their skin. These 

 remains are chiefly interesting as indications that two of the 

 great leading divisions of the class of fishes originated together. 

 In the Devonian age the Ganoids and Sharks, thus introduced 

 in the Silurian, may be said to culminate. The former, more 



