430 Evolution and Distribution of Fishes 



during later geologic periods. These all apparently evolved 

 from a few individuals which multiplied so recently in the 

 geologic history of the continent, that they were all re- 

 tained west of the rift-valley walls and of the Great Central 

 Mountain Chain. 



It is extremely likely that the ancient family Albulidae 

 started in the early Cretaceous period, as a marine deriva- 

 tive from like ancestry with all of the above. For though 

 it must be confessed that, apart from structural details that 

 ally it with the above families, we have absolutely no good 

 proof that they were ever freshwater. The close affinities 

 shown with Notopteridae, Osteoglossidae and Mormyridae 

 are in themselves a strong argument in favor of their being 

 descended from a common ancestor with these. The exist- 

 ence of several species of Anogmius in the marine Cretaceous 

 Niobrara beds of N. America, of Prochanos, Istieus and 

 related genera in the Cretaceous of central S. Europe, and 

 of others in more recent south and central European beds, 

 might be explained by our viewing all of these as early 

 derivatives from some freshwater ancestors of Lower Cre- 

 taceous age that were common and ancestral for all of 

 the above families. 



