284 Evolution and Distribution of Fishes 



of which the teeth, scales, etc. are so common in the coal 

 shales and cannels of England and Scotland." 



But as with the European fauna so here, an abundant 

 migration seaward of freshwater species, and evolution 

 of many marine types subsequently took place. A rich 

 locality for these fossils is the North Central or Illinois 

 Coal Field, from the marine Carboniferous Limestone of 

 which Newberry, Worthen and St. John have described 

 upwards of 300 species." {g8: 2og; v.4, v.7). As with 

 the list of Davis in comparison with that of Young, so here, 

 certain of the genera were purely freshwater, others were 

 marine, while not a few were anadromous. If we may 

 safely judge from those that are associated with chondros- 

 tean and ganoid fishes, also with amphibians, the number of 

 freshwater species amounts to about thirty, while anadrom- 

 ous ones are still more abundant. So for the American as 

 for the European land area, an extensive seaward migra- 

 tion of elasmobranchs had evidently taken place in late 

 Devonian or early Mississippian time, and many new spec- 

 ies as well as genera subsequently evolved as anadromous 

 or as wholly marine forms. 



In regard to the succession of strata that contain these 

 fishes, the lowermost or Bedford Shale, that rests on the 

 freshwater Cleveland Shale, is largely, possibly wholly, 

 marine. The Berea Grit in its lower part is also, but it 

 becomes, in the Chagrin Falls region freshwater, and con- 

 tains abundant remains of the equisetoid Anniilaria^ of the 

 freshwater chondrostean fishes Palaeoniscus and Ctena- 

 canthus. But we yet await, for American strata as a whole, 

 lists that may as accurately determine the distribution of 

 elasmobranchs, as do those of Davis, Young, Traquair, 

 Atthey and others for European strata. 



Reviewing now the above, and many other records 

 which cannot here be dealt with, the writer would conclude 

 that in late Old Red or Devonian, and specially in early 

 Carboniferous time, primitive elasmobranchs attained to 

 enormous development, alike in species and individuals, in 

 freshwater lakes, rivers, and swamps. Much of the litera- 

 ture — we might well say nearly all of it — of the past has 

 accepted it, without proper proof, that they were marine, 



