256 THE HABITAT OF THE EURYPTERIDA 



On the other hand, these peculiarities are easily understood, if we 

 consider the eurypterids as fluviatile organisms. It is quite evident 

 that the Kokomo deposits have a distinctly different source from 

 those of the Bertie. If then, these eurypterids belong to a distinct 

 river system, developed upon a separate land mass, it would indeed 

 be surprising if they were not wholly distinct specifically from those 

 of the rivers of Atlantica which were responsible for the Bertie water- 

 lime deposits. The alternation of beds with marine fossils with beds 

 carrying only eurypterids and ceratiocarids, suggests that the Ko- 

 komo deposits may have approached those of some modern estu- 

 aries in which we have an alternation of marine and fresh- water 

 deposits. The map, Fig. 8, shows the position and general extent of 

 these late Siluric river systems. 



CONCLUDING REMARKS 



When the significance of the distribution and of the occurrence 

 of the eurypterids is given its full importance, there can no longer be 

 any doubt that the eurypterids at no time of their known history 

 were normally marine organisms. We cannot conceive of marine 

 animals presenting such localized occurrences and yet having such 

 wide distribution as a class. The question of transit seems not to 

 have been considered by previous authors, and yet it is one of the 

 greatest importance. If we suppose that the eurypterids lived in the 

 Palaeozoic rivers, we have furnished them with the proper milieu for 

 individual as well as racial development. For we must not overlook 

 the fact that when these animals make their appearance in numbers, 

 they are already highly differentiated. To a river dweller migrations 

 from the headwaters of one river system to those of another are easily 

 possible, and this is the only way by which we can account for the 

 distribution of these organisms, unless we assume migrations along 

 continuous shore lines which is, however, negatived by the lack of 

 remains in the shore deposits of the period in which they most abound. 

 Furthermore, the segregation into "pools" can be accounted for only 

 by assuming that these "pools" were fed each by its own river system. 

 A candid and unbiased survey of the facts presented cannot but lead 

 to the unqualified belief in the fluviatile habits of these remarkable 

 arthropods of the Palaeozoic era of the earth's history. 



