The Primitive Fishes 283 



more primitive forms, that are of holostean descent, gradu- 

 al transition is made through Cleithrolepis and Dapedius 

 to Microdon and Mesodon, thence to Coelodus and Palaeo- 

 balistum. A like parellelism is shown by several groups 

 of the bony fishes. 



In regard to American palaeozoic elasmobranchs, New- 

 berry seems clearly to have reached the conclusion — in 

 marked contrast to that formed by him about Devonian 

 elasmobranchs and more ancient fishes — that not a few 

 of these originated as, and remained as, freshwater in- 

 habitants. Some of them also must have been large and 

 striking forms. Speaking of the Ohio Coal strata {S6: 

 211) he says: "The Linton locality is specially interesting 

 and instructive. It has already yielded more than twenty 

 species of fishes, and nearly forty species of aquatic am- 

 phibians, all inhabitants of the same body of water. These 

 are found in a thin stratum of cannel which, over a limited 

 area, underlies a thick bed of cubical coal (No, 6 of the 

 Ohio Reports), of which the place is near the top of the 

 Lower Coal Measures," and later he adds, "we have evi- 

 dence that the great marsh in which the peat accumulated 

 that formed Coal No. 6 was for a time a lake or lagoon, 

 inhabited by the fishes and amphibians to which I have 

 referred," 



Probably the most striking genus is that named Edestus 

 by Leidy, and which is found in the Mississippi-Illinois 

 coal fields. It was minutely studied by Miss Hitchcock, 

 Leidy, Newberry, Hussakof, but was properly interpreted 

 by Eastman {208 : 281). The remains consist of bony jaw- 

 plates that bear often large serrated teeth. These indi- 

 cate the existence of a large selachian fish in the 

 eastern American Coal-fields that must have been 8 ft. 

 to 10 ft. in length. They occur in a bituminous shale that 

 "is apparently a freshwater sediment," while the associated 

 fossils include a large number of fish teeth, some of which 

 belong to carnivorous sharks, as Cladodus and Petalodtis ; 

 and others with crushing teeth which probably fed on hard- 

 shelled molluscs, as Orodiis, Orthopleurodits etc, "The 

 habitat of Edestus would therefore seem to have been 

 somewhat similar to that of Rhizodus and Megalichthys, 



