WERE LAID DOWN 



Canada ; and there is little doubt that in all these places 

 there were great lakes which gradually became the deposi- 

 tories of rivers and developed a life of their own. 



The most remarkable fossils of these deposits were the 

 fishes. The fishes began to appear in the later Silurian : 

 they are strikingly abundant in Devonian times. The 

 most remarkable of them are fishes which are only just 

 like fishes after having been developed out of, or perhaps 

 descending from, some other form of life. These fishes 

 are now called the Ostracoderm group, and they bear 

 strange resemblance to some of the trilobites and the 

 king crabs of previous eras. The Pteraspis is one of 

 the earliest of these strange creatures, and its "fins," very 

 much developed, were used as oars. Perhaps the most 

 curious of all these strange creatures were the Pterich- 

 ihyds or winged fish ; though it is not at all likely that the 

 appendages we call wings were used for aerial flight. These 

 fishes were all small ; their forms were clumsy and their 

 powers of moving about small. They had poor mouths 

 and eyes, and they probably ploughed the soft bottoms of 

 the sluggish waters, above which little besides their pecu- 

 liarly placed eyes and the backs of their plated bucklers 

 were habitually exposed. Another strange class of fish- 

 like creatures was represented by a little creature which 

 was found in Scotland and is sometimes supposed to be 

 the ancestor of the lamprey. 



Besides the fresh-water fishes there were some which 

 dwelt in the sea ; but in the Devonian era the fresh-water 

 fishes were far more numerous. We cannot mention them 

 all. The fish called Coccosteus and its allies had great bony 



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