Distribution of PRiMifiVE Fishes 499 



Illinois, and even Nebraska coal fields. Still later in the 

 Permian beds of France, Rhenish Prussia, Silesia, and Bohe- 

 mia on the east, also in those of Illinois and Texas, remains 

 of the genus are frequent. Now over this entire area the 

 associated organisms are freshwater, and all traces of 

 marine organisms are absent. So the facts seem fully to 

 warrant the conclusion that the Pleuracanthidae started in 

 some lake or river habitat of Central Europe, during the 

 deposition of the earlier beds of the Calciferous system, 

 but radiated outward till Bohemia on the east and Illinois- 

 Nebraska-Texas on the West, had been peopled with at 

 times teeming individuals belonging to some one species of 

 the genus. For these then as for the Acanthodii, we would 

 only repeat the closing part of last paragraph : "they never 

 transgressed the limits of the N. Atlantis Continent." 



In closing this chapter it may not be inappropriate to 

 sum up some of the positions reached in the above inquiry. 



First: Unless future discoveries in southern continental 

 areas entirely change our present knowledge, it can be said 

 that all existing evidence points to the conclusion that fish 

 life originated in freshwaters of a wide northern continental 

 mass, which by Freeh and others has been called North 

 Atlantis. 



Second: This continent extended, during late Silurian 

 and Devonian times, from W. Russia and E. Germany, to 

 Canada and the N. E. United States. Though furnishing 

 no evidence of high elevations (above 2000-3000 feet), nor 

 of surrounding great ocean depths, it had a widely develop- 

 ed intrinsic system of rivers, lakes, and flood-plain areas 

 that permitted gradual extension from a focal centre some- 

 where between N. E. Scotland and W. Russia, of evolving 

 genera and often even of species that represented primitive 

 freshwater fishes. So by "Old Red" and Carboniferous 

 times or even earlier, genera like Thelodus, Cephalaspis, 

 Bothriolepis, Acanthodes, Pleiiracanthus, Dipterus, and 

 Sagenodus had become continuous in habitat over the above 

 continent. 



Third: Most of these primitive fishes were clumsy and 

 sluggish in response reaction, were often cumbered by a 

 heavy bony coat of mail, and seem to have been bottom- 



