SKELETON OF LEPIDOSTEUS. 461 



which resemble the Prtl0eonisclda3 in form, shape of the fins, size 

 of the month, and structure of the teeth. 



In comparing Eugnathus with Pcdceoniscus, both strong- 

 swimming predacious fishes, it is not evident that emy of the 

 differences between them are adaptative. But these differ- 

 ences are due to the Semionotid ancestry of the Eugnathidse, 

 and there is good reason for believing that they were adapta- 

 tive in origin. 



The later evolution of the Neopterygian Fishes offers numbers 

 of parallel examples : modifications persist and become the basis 

 for further modifications. 



