EXTINCT ANIMALS 



survivor. One of these ancient forebears of 

 the Ceratodus is found fossil in the Devonian 

 or Old Ked Sandstone of Scotland and of 



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Russia. It is known as Dipterus, and is shown 

 in Fig. 182. It differs from Ceratodus in having 

 strong bony scales (whence its preservation as 



250 



