98 THE STORY OF THE EARTH AND MAN. 



Ptenchtliijs, with its two strong bony fins at the sides, 

 which may have served for swimming, but probably 

 also for defence, and for creeping on or shovelling 

 up the mud at the bottom of the sea. But, besides 

 the Ganoids which were armed in plated cuirasses, 

 there were others, active and voracious, clad in 

 shining enamelled scales, like the bony pikes of the 

 American rivers and the Folypferits of the Nile. 

 Some of these, like the Diplacanthus, or " double- 

 spine," were of small size, and chiefly remarkable 

 for their sharp defensive bony spines. Others, like 

 Holoptycliius (wrinkled-scale) and Osteolepis (bone- 

 scale), were strongly built, and sometimes of great 

 size. One Kussian species of Asterolepis (star-scale) 

 is supposed to have been twenty feet in length, and 

 furnished with strong and trenchant teeth in two 

 rows. These great fishes afi'ord a good reason for 

 the spines and armour-plates of the contemporary 

 trilobites and smaller fishes. Just as man has been 

 endeavouring to invent armour impenetrable to shot, 

 for soldiers and for ships, and, on the other hand, 

 shot and shells that can penetrate any armour, so 

 nature has always presented the spectacle of the 

 most perfect defensive apparatus matched with the 

 most perfect weapons for destruction. In the class 

 of fishes, no age of the world is more eminent in 

 these respects than the Devonian.* In addition 



* Many of these were discovered and successfully displayed 

 and described by Hugh Miller, and are graphically portrayed 

 in his celebrated work on the *' Old Ked Sandstone," puplished 

 in 1841. 



