The Soft-finned Teleostei • 365 



Individuals and species, they almost surely were the centres 

 also for evolution of new connecting genera and families 

 of teleosts. 



It may also be emphasized here, and will be returned 

 to later, that In this region was the organic centre for the 

 Aphredoderldae, usually made a small freshwater division 

 of the marine Berycidae, but which during lower Eocene 

 and later times Included such freshwater genera asAmphi- 

 pJaga, Asineops, Erismatoptenis, Trichophanes, and Is now 

 represented by the single species Aph?-edoderus sayanus of 

 the Mississippi valley and eastward. 



The true interpretation for the family evidently is that 

 it combines transition characters from the Sa^monidae- 

 Clupeidae to the Haplomi, and thence on to the Percidae 

 and Berycidae, while the past and present distribution of 

 the genera strongly indicate that the N. American lakes 

 formed a great organic focal centre in which freshwater, 

 and in some cases what later became marine, families 

 evolved, and then radiated out. 



The alliance of families that Ichthyologists have united 

 as the Hemibranchil, CatosteomI, Thoracostei or Phthlno- 

 branchll, is a transition series between the soft-finned and the 

 spiny-finned fishes that are of great interest, alike from the 

 structural, palaeontologlcal and distributional standpoints. 

 Though unknown in the fossil state the Gastrosteidae or 

 Sticklebacks, Indicate equally by their generalized structure 

 and practically continuous distribution over freshwater 

 regions of the Northern Hemisphere, that they are a very 

 ancient family. The presence also. In Upper Eocene and 

 In Miocene strata, of freshwater species of the allied but 

 greatly more specialized families Aulorhynchidae, Flstu- 

 larlidae, Centrlscidae, and Syngnathldae that are now whol- 

 ly marine, is also highly suggestive. The writer would 

 propose the following as explanatory for the gradual evolu- 

 tion and distribution of the entire group. 



Derived, like Pseiidoberyx, also like the Percopsidae, 

 and the Aphredoderldae, from a more primitive clupeo- 

 salmonid stock, the five genera of Stickleback, namely 

 Gastrosteus, Pygosteus, Apeltes Eiicalia and Spinachia, are 

 met with in streams, pools and ponds across the entire North 



