The Dipneusti and Crossopterygii 307 



lists of marine elasmobranchs of the period, as given by 

 Davis, by Young, and by Traquair (77: 693,696). But the 

 last named author, in dealing with the problem, speaks 

 throughout of "marine fishes" and "estuarine fishes." Not 

 one fact however in the above and in many other papers by 

 him, favors the idea even of "estuarine conditions," which 

 have bulked greatly too much in geological and palaeonto- 

 logical literature. He gives rich lists from the Calciferous 

 beds, which in all of their connections and indications are 

 freshwater. These include MegaVichthys, Rhizodus, Strep- 

 sodiis as well as Tarrasius from Eskdale; he gives from the 

 "Edge Coal" Megalichthys, Rhizodus, Strepsodus, Rhizod- 

 opsis and Coelacanthus; also from the Coal Measures Meg- 

 alichthys, Rhizodopsis, Strepsodus, and Coelacanthus. 



While the elasmobranchs then sent numerous out- 

 liers into the sea during the period at present under con- 

 sideration, there seems no reliable evidence for accepting 

 it that a single genus of crossopterygians migrated into 

 marine surroundings. 



The genera that are named together above show, so far 

 as known, varying distributional ranges. Thus Tarrasius is 

 peculiar to the Calciferous, Rhizodus to the Calciferous 

 and freshwater ironstone-shale beds of the Lower Carboni- 

 ferous, Strepsodus ranges from Calciferous to Coal Meas- 

 ure strata, Rhizodopsis occurs only in the Coal Measures 

 from Silesia to Britain, and thence on to Nova Scotia, while 

 Megalichthys and Coelacanthus extended from the Calci- 

 ferous up to the Permian. But all disappear with the 

 Upper Permian, to be replaced by other genera that are 

 discussed below. 



The Crossopterygians of the European Coal Measures 

 were evidently able to spread by some freshwater line of 

 travel to America, for two species of Rhizodus {Megalich- 

 thys of Agassiz and Hibbert) and three species of Coela- 

 canthus, as well as scant remains of the true Megalichthys 

 were early described by Newberry from the Ohio coal 

 fields. In referring to them and other organisms he says 

 that they were "from a single locality, which has already 

 become somewhat celebrated for the number and interest 

 of the fossil forms it has furnished. I refer to Linton on 



