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 The Permic of Portugal has furnished the final straggler of the race in a small Eurypterus [de Lima, 1890].

A very interesting problem in the study of the eurypterids is that of their bionomic relations and geologic facies. A philosophic contribution to the discussion of this problem has been given by Professor Chamberlin in his paper On the Habitat of the Early Vertebrates [1900, p. 400].

Chamberlin's hypothesis is to the effect that "the fish and the eurypterids descended from the rivers to the sea in the mid-Paleozoic, though their remote ancestors may have ascended from it," and the principal argument in its support is found in the claim that "there is only one conspicuous type that is facilely suited to free life, independent of the bottom, in swift streams, and that is the fish form"; it is further urged that "this could have developed only in water that possesses a persistent and usually rather rapid motion in a fixed direction, i. e., in rivers."

In support of this hypothesis it is pointed out that the Paleozoic fish and the similarly built eurypterids are always associated and it is suggested that the two possessed a parallel development due to the same physical influence. This view of the fresh-water origin of the eurypterids is directly contradictory to the current view among paleontologists of their originally marine habitat and later adoption of first a brackish and finally a freshwater life. Zittel-Eastman's Textbook of Paleontology expresses this prevailing view as follows [1896, p. 673]:

They are found associated with graptolites, cephalopods, and trilobites in the Ordovician of Bohemia and North America; with marine Crustacea (Phyllocarids and Ostracods) in the Silurian; with Ostracoderms and Arthrodires in the Devonian; and with land plants, scorpions, insects, fishes and fresh-water amphibians in the Productive Coal Measures. It is apparent, therefore, that from being originally marine forms, they became gradually adapted to brackish, and possibly even fresh-water conditions.