The Chondrostei and Holostei 321 



first appearance in the Calciferous of Britain, Belgium, 

 and Nova Scotia {A. hortonensis) , on through the Coal 

 Measures and into the Permian of Russia, Germany, Brit- 

 ain, and probably also into the Karoo beds of South Africa 

 (//. fdigitata) is proof that extensive intercontinental areas 

 of freshwater existed. The species of Elonichthys also al- 

 most equal the last. 



At times it seems as if areas had existed for evolution 

 of new genera or species, alongside others of wider dis- 

 tribution. Thus Newberry described at least four species 

 of a new genus Eurylepis^ in the richly fossiliferous beds 

 near Linton, Ohio, that were associated with species of 

 Palaeoniscus, Rhizodus, Coelacanthus, etc. (25^:347), 

 that all inhabited according to the author "rivers, lagoons, 

 lakes, and bays." 



On passing up to the Permian and Triassic beds 

 palaeoniscid life seems to have received a great check early 

 in the former period, accompanied by obliteration of most 

 of the genera, possibly owing to the coming on of wide- 

 spread xerophytic conditions, but mainly to frequently in- 

 termittent volcanic outbursts, succeeded by active and wide- 

 spread denundation action. As a result Amhlyptenis and 

 Palaeoniscus — rich in species and individuals — as well as 

 the rarer Pygopterns and Trachelacanthiis disappeared in 

 the epoch during which they evolved. But their places 

 were taken in Triassic times by Gyrolepis^ Apateolepis, 

 Myriolepis, Urolepis^ and Atherstonia, which, as a group 

 of genera, extended from North Central Europe to South 

 Africa and Australia. These organisms, as well as the 

 deposits in which they occur, are acknowledged to be of 

 freshwater origin. 



Such genera however, in dying out, were replaced by 

 Oxygnathiis, Centrolepis, and Coccolepis, during Lower 

 Liassic days, while the third of these endured even as a 

 lingering remnant into Lower Kimmeridgean strata. From 

 their occurrence alongside other undoubtedly freshwater 

 fishes, and their presence in lower Liassic shales devoid of 

 marine remains, Oxygnathus and Centrolepis continued to 

 be freshwater in habitat like all of their ancestral allies. 

 As to Coccolepis one species C. liassica occurs in the same 



