272 Evolution and Distribution of Fishes 



In time-extension remains of spe- 

 cies occur from Lower Carbonifer- 

 ous to Lower Permian beds, and in 

 space-extension they are found from 

 Nova Scotia, Illinois and Ohio 

 through Britain and France to Prus- 

 sia, Silesia and Bohemia in Europe. 

 A species even has been described 

 from the freshwater Hawkesbury 

 beds of New South Wales. But 

 if — as seems likely — the isolated 

 teeth, that have been called Clad- 

 odus, belong to pleuracanthid fishes, 

 then the group first appears in fresh- 

 water strata of Mid-Devonian age 

 in Eastern America. 



Davis (7/0:321), after discus- 

 sing the affinities of Pleiiracanthus 

 referred to several species, and 

 "argued that both Co el acanthus and 

 Pleiiracanthus were probably fresh- 

 water fishes, the former possessed of 

 an air-bladder." Brongniart and 

 Sauvage also agree {20 1) that 

 Pleiiracanthus gaudryi is like the 

 other fishes of the Commentry de- 

 posit of freshwater habitat. 



So Pleiiracanthus, with which — 

 following Egerton, Fritsch and oth- 

 ers — we unite Comps acanthus, Orth- 

 acanthus, Xenacanthus and Diplo- 

 dus, is everywhere a freshwater 

 genus. For the entire assemblage 

 of organisms in the Borough Lee 

 rocks near Edinburgh; those from 

 Middle or Upper Coal Measures of 

 Lanark, Northumberland, York and 

 Staffordshire in England; most of 

 the fish-bearing beds of Ohio and 

 Illinois; and the Gaskohle of Bo- 



