3o6 Evolution and Distribution of Fishes 



beds, alike lithologically and in their organisms. But in 

 addition to like genera of fishes, there occur in the same 

 strata abundant impressions of Adiantites and the fresh- 

 water mollusc Anodonta jukesii. He therefore says: "It 

 is abundantly clear that lacustrine conditions prevailed over 

 this area of the south of Ireland, during the deposition 

 of these beds, and that thus by their fossils and physical 

 relations they correspond with the deposits of those great 

 inland lakes already referred to." 



It would seem as if the Canadian and the States fishes 

 had originated in, and had gradually spread westward 

 from, the North European Old Red areas, for while the 

 subgenus Glyptolepis of the genus Holoptychhis occurs in 

 the lower Old Red of Scotland as G. leptopteriis, it appears 

 in the upper Old Red of Scaumenac Bay, as G. qiiebecensis. 

 A like retarded developmental distribution has been re- 

 peatedly noted for other types. The finding by Newberry 

 of Onychodiis sigmoides^ and of Holoptychius scales, in 

 the Ohio and Onondaga rocks, indicates that rapid migra- 

 tion from Europe westward was then proceeding, while 

 from the Chemung-Catskill series eight or nine species of 

 holoptychlan remains have been described. 



But as already noted for the Dipneusti, a wide extension 

 of the freshwater basins took place in central North 

 America, so that remains of Onychodus and Holoptychius 

 have been obtained from Iowa and Colorado. 



In all cases examined by the writer the beds in which the 

 above genera occur are clearly freshwater, as are those of 

 the Lower Old Red. For the absence of marine remains, 

 the increasing frequency of a flora mixed with the fishes 

 that is prophetic of the Carboniferous formation, alike 

 in its types and in its richness, also the frequent continuity 

 in genera that are clearly freshwater in the Lower, and 

 continue so to the Upper, are all powerful arguments. 



With transition from Old Red to Carboniferous rocks, 

 a complete change in crossopterygian genera takes place, 

 so that while all of the above are blotted out, their place 

 is taken by Tarrasius^ Rh'izodus, Rhizodopsis, Megalich- 

 thys^ and Coelacanthus. In regard to these it may at once 

 be said that all of them are entirely absent from the varied 



