BUFFALO SOCIETY OF NATURAL SCIENCES 213 



The question is generally answered by the statement that the eu- 

 rypterids originally lived in the sea and then migrated to the various 

 marginal water bodies and estuaries where they and a few peculiar 

 crustaceans constituted a brackish water fauna. I have already 

 shown (p. 70) that a ''brackish water" fauna consists of modified 

 marine and freshwater euryhaline organisms with a preponderance 

 of marine types, and that the latter show particular characteristics 

 such as dwarfing and thinning of the shell, but that such a fauna has 

 representatives of nearly all invertebrate phyla and is not made up 

 of a single class of organisms. But let us assume for the sake of ar- 

 gument that the eurypterids and a few other arthropods did form a 

 brackish water fauna; then another assumption is necessary, for, if 

 a class of organisms as a whole, such as the eurypterids, should in any 

 given geological period migrate from the sea to estuaries or other 

 brackish water bodies and at the same time should no longer be able 

 to live in the sea, and should not, on the other hand, become adapted 

 to river water, then the remains of such a class of organisms should 

 be restricted to the geological period in which the migration took 

 place, for the class could not persist unless the estuaries persisted 

 from period to period in the same locality (see objection to this on 

 p. 215 below). 



But since the class is known to have persisted from period to per- 

 iod, as indicated by the occurrences of their remains in the rocks, we 

 are forced to conclude, on the assumption that the organisms mi- 

 grated from the sea to the estuaries, that there was a persistent marine 

 stock to repeople each successive estuary. But, if that were true, 

 then eurypterid remains of the same or allied species should be found 

 entombed with the marine organisms of the period in the marine equiv- 

 alents of the estuarine or other brackish water deposits, and the euryp- 

 terids should have constituted a part of the typical marine fauna. 

 But it has been shown again and again that in the contemporaneous 

 marine deposits with typical and undoubted marine faunas, no euryp- 

 terids are found, as, for instance, in the marine Wenlock of England, 

 or the marine limestones of the Famennian of Germany. If there is 

 no indication of such a persistent marine stock, then there must have 

 been a persistent stock in the rivers to repeople the estuaries in the 

 successive geologic periods. These arguments may be applied spe- 

 cifically to the Siluric and Devonic of North America. During the 

 Lower Siluric (Niagaran), the eurypterids are supposed to have lived 

 in the sea. During the remainder of the Siluric they are assumed to 



