270 Evolution and Distribution of Fishes 



then evolved in the freshwaters of Eastern America, while 

 as yet no trace of them has been met with in marine beds. 



Attention may next be drawn to the list of fishes re- 

 corded from the Lower Devonian freshwater beds of Camp- 

 bellton (N.B. Canada). These, as listed by Eastman 

 {ig8 : 2j ^) include the following elasmobranchs and chi- 

 maeroids: Acanthodes semistriatus, Climatius latispinosiis, 

 Gyracanthus incurvus, Protodus jexi, Doliodus problemati- 

 cus, Cheir acanthus costellatus, Homacanthus gracilis, and 

 Machaeracanthtis sulcatus. 



In comparing the above lists it is of interest to find 

 that while the species may be different, such genera as Acan- 

 thodes, Climatius, Cladodus, and others are common to 

 the freshwater strata of Canada, the Eastern States and 

 Europe. 



The Chemung and Catskill strata seem at least in part 

 to have had freshwater origin, for such genera as Dipterus, 

 Dinichthys, Onychodus, and Holoptychius were wholly 

 freshwater in habitat. These along with the freshwater 

 moWusc A no dont a, and with the plant genera Archaeopteris, 

 Sigillaria, and Lepidodendron strongly suggest that while 

 the Chemung may be regarded as Upper Devonian, the 

 Catskill, like the Cleveland shale, possibly merges into 

 Mississippian or Lower Carboniferous. Regarding it 

 Chamberlin (^:434) says: "The Catskill formation is 

 suflEciently different from the rest of the Upper Devonian 

 to indicate that the sediments of which it is composed ac- 

 cumulated under conditions very different from those which 

 obtained further west. This formation is poor in fossils, 

 and such as occur are partly, if not wholly, of fresh- and 

 brakish-water forms. Hence it is inferred that the Catskill 

 region was at least so far shut off from the ocean as not 

 to afford the conditions necessary for marine life. The 

 formation is notable for its redness, a feature which marks 

 many other formations made in inclosed or partly in- 

 closed seas, inland lakes, or basins." 



The above extended, but highly necessary digression, 

 is partial proof that species of Acanthodes, Climatius and 

 other primitive elasmobranchs had gradually evolved over 

 some fairly continuous northern area of land. In this area 



