96 THE STORY OP THE EARTH AND MAN. 



practically the Eurypterids of the modern ocean. So 

 change the dynasties of men and animals. 



".Thou takest away their breath, they die, 



They return to their dust ; 

 Thou sendest forth Thy Spirit, 



They are created ; 

 Thou renewest the form of the earth." 



The reign of fishes began in the Upper Silurian, for 

 in the rocks of this age, more especially in England, 

 several species have been found. They occur, how- 

 ever, only in the newer beds of this formation, and 

 are not of large size, nor very abundant. It is to be 

 observed that, in so far as the fragments discovered 

 can be interpreted, they indicate the existence already 

 of two distinct types of fishes, the Ganoids, or gar- 

 fishes, protected with bony plates and scales, and the 

 Placoids, or shark-like fishes ; and that in the existing 

 world these fishes are regarded as occupying a high 

 place in their class. Further, these two groups of 

 fishes are those which throughout a large portion of 

 geological time continue to prevail to the exclusion 

 of other types, the ordinary bony fishes having been 

 introduced only in comparatively recent periods. 

 With the Devonian, however, there comes a vast 

 increase to the finny armies ; and so characteristic 

 are these that the Devonian has been called the age 

 of fishes par excellence, and we must try, with the 

 help of our illustration, to paint these old inhabitants 

 of the waters as distinctly as we can. Among the 



