5i8 Evolution and Distribution of Fishes 



others have listed marine elasmobranchs. Occasional mix- 

 ing of records however, or mistaken identification, by some 

 authors, are recorded, and such have given rise to incorrect 

 conclusions. Generic continuity of life conditions from 

 Carboniferous to Permian is proved by the presence of 

 Megalichthys and Coelacanthus in lower, or even in upper 

 Permian rocks of Germany, England and Texas. 



But new and more evolved genera — at times however 

 devolving ones — continue the group to Triassic and on 

 even to Jurassic age, alike in the Old and New Worlds. All 

 of these, like Dipliirus, Heptanema, and Undina were fresh- 

 water dwellers. But while the New World fishes have been 

 so accepted, the mistake has been made of regarding those 

 from the Austrian and Italian bituminous strata as marine. 

 All resembled each other in their environal habitat. 



One genus however, Macropoma. according to all pre- 

 sent evidence either became wholly marine by the time of 

 the Lower Chalk, or if anadromous it seems to have been 

 more abundant in marine than in estuarine or fresh waters. 

 The only surviving genera Polyptertis and Calamichthys of 

 Central Africa are lingering remnants of a once large, but 

 now disappearing group. 



Chapter ii. The Chondrostei and Holostei in time and 

 space. 



The above two groups of ganoid fishes "rank next in 

 time of appearance and structure to those already" re- 

 viewed. For the occurrence of only one genus in Old Red 

 rocks, the more perfectly ossified skeleton, the usually hete- 

 rocercal or homocercal tail fin, are in part confirmatory. 

 After short reference to the distribution of the four or five 

 living genera of Chondrostei and to the pioneer Old Red 

 genus Cheirolepis, the numerous genera of Calciferous or 

 lower Misslssippian age like Elonichthys, Acrolepis, and 

 others are invariably freshwater, as already emphasized. So 

 they are absent from marine lists. The fact that these and 

 the older Cheirolepis are known from North Britam to Rus- 

 sia, and that their modified descendants appear chiefly in 

 higher and later coal beds of Canada and the States, also in 

 the Karoo beds of S. Africa, Indicates that the same lines of 



