The Soft-finned Teleostei 361 



rivers and lakes; also of the Enchodontidae — which disap- 

 peared at close of the Cretaceous — likewise of the Scope- 

 lidae, Aleposaurldae, Chirothricidae, and Stephanoberyci- 

 dae, that gradually spread into marine environment. 



The most ancient now known is the Enchodontidae, 

 which seems to be made up typically of marine animals. 

 Whence derived it is impossible to say till connecting links 

 between "ganoids" and the modern Haplomi are obtained. 

 All of them disappeared during the cataclysmic period that 

 brought to a close eastern Cretaceous deposits. But the 

 view is generally accepted that the Aleposauridae of the 

 Scopelidae are near living examples. 



The natural group of families that has in recent years 

 been called the Heteromi or Notacanthiformes is evidently 

 a very ancient one. For three of the five component fami- 

 lies, viz Dercetidae, Halosaurldae, and Notacanthidae are 

 all encountered in upper Cretaceous marine rocks from 

 central Europe south-ward to Lebanon. But like the 

 Enchodontidae they are also found in the Cretaceous of 

 N. America. Now since apparently reliable remains of 

 Enchodus have been described from the Greensand, also 

 from the Niobrara of N. America and from still higher 

 strata of Mid-Europe, it seems not unlikely that all evolved 

 from some still earlier clupeo-salmonid freshwater ancestor 

 of western North America. In the living forms the air- 

 bladder is still retained, but is a closed sac. 



The Scopelidae were well represented in the Cretaceous 

 by at least ten genera, and the Chirothricidae by three, all 

 of which disappeared at the close of the period. But evolv- 

 ing collateral descendants must have carried both families 

 on into Eocene and later periods. So the full century of 

 living species are known only as marine inhabitants. Many 

 also of them are highly modified, in structure and in 

 phosphorescent material, as deep-sea fishes. 



Like remarks apply to the usually highly modified 

 Stephanoberycidae and Aleposauridae, all of which are, 

 and seem through long past time to have been, marine. 

 It seems impossible however at present to trace their earli- 

 est derivation from ganoid ancestors. But it may be added 

 that a gradual absorption of the air-bladder is proceeding 



