were prevailingly inhabitants of the brackish water zone, and in Devonic time they were wholly so.
In the Carbonic era on this continent the eurypterids are mainly perpetuated by the peculiar subgenus Anthraconectes, in the Productive Coal Measures. These are found in Pennsylvania on slabs densely covered with fern leaves and other plant remains which can not fail to suggest near land and probable fresh-water conditions. Yet even in this case, the fragmentary condition of many of the fern leaves which would, according to the criteria of the "Allochthonie" of the coal measures, advanced by Potonié[1] indicate the transported condition of the material; even more the profuse presence of the small spiral tubes of the marine Spirorbis on the plant remains, as shown by Simpson's excellent figure [Hall, 1884, pl. 6] afford a caution against an unqualified conclusion as to the fresh-water habit of these Carbonic eurypterids. In a recent exhaustive discussion, Girty[2] has reached the conclusion that it seems most reasonable to regard the fauna of the Carbonic of Pennsylvania "as a natural assemblage of species selected and modified by a habitat, if not in strictly marine, at least not in strictly fresh waters."
There is, however, clear evidence at hand of the fresh-water habitat of the Carbonic eurypterids in other regions. One of these is the occurrence of Eurypterus (Adelophthalmus) granosus Jordan in the coal measures of Saarbrücken. That basin was formed in the interior of a continent and never reached by the sea.[3] In other coal basins, notably those of England[4] the gradual freshening of the lagoons and the disappearance of such marine types as Lingula and Orbiculoidea, which are frequent in the lower coal measures, has been clearly recognized. It is only in the upper measures that the eurypterids occur, there in association with ostracods, phyllopods and schizopod crustaceans. Woodward [1879,
