354 Evolution and Distribution of Fishes 



from America eastward, a correct and sure basis is secured 

 for future explanation and fitting together of morphologic, 

 physiologic, taxonomic, and geographic facts that hitherto 

 have been uncorrelated and inexplicable. 



With advent of the Mid and Upper Cretaceous periods, 

 a rich teleost fauna unfolded. For from Cenomanian and 

 specially Turonian age, upward to the close of the Cretace- 

 ous, more than 50 genera have been described. The origin 

 of these also proceeded from various more primitive ganoid 

 stocks. Thus the Elopidae exhibit close structural re- 

 semblances to the freshwater amioid Megaliirus of Kim- 

 meridgean and Purbeck rocks. By mid and upper Cretace- 

 ous times however nine or ten genera had appeared in 

 abundance from west-central America to central Europe, 

 most or all of which must have migrated seaward during 

 Neocomian to Gault time. But that they still show de- 

 cided freshwater affinity is strongly indicated by the fact 

 that the young and the adults of Flops and Megalops still 

 enter rivers freely. 



Other families of probably primitive amioid ancestry, or 

 that are derived from some intermediate type between the 

 Eugnathidae and Amiidae are the Albulidae, and the Osteo- 

 glossidae, the former of which took to a marine life even 

 during the Cretaceous age. So from some early Cretaceous 

 genus of the former family the widely distributed Albiila 

 {Butirinus) of tropical seas, and the deepsea genus Ptero- 

 thrissus, that closely resembles Istieiis of Cretaceous age, 

 seem to have originated. 



From the latter and still purely freshwater family, 

 Osteoglossidae, derivative genera like Dapedoglossus of the 

 U. S. Green River shales, and Brychaetiis of the London 

 Clay lead up to the four existing genera Osteoglossum and 

 Arapaima of S. America, Heterotis of Central Africa, and 

 Scleropages of Malaya and N. Australia. The distribution 

 of these is of exceptional interest, and resembles many other 

 like cases referred to in subsequent pages. For from some 

 S. American ally of the known N. American Dapedoglossus 

 derivative types seem rapidly to have spread over the lakes, 

 swamps and sluggish rivers of the Gondwana continent, and 

 then multiplying in localized centres of it originated other 



