not Crustacea, but belong to the class Arachnida. The work has only just begun of convincing that same geological world that the habitat never was marine, but always fluviatile.
For nearly fifty years after Conrad made his statement authors described new species, erected new genera and worked out the affinities of the eurypterids to Limulus, but they gave not a thought to the habitat. It was not until 1889 that a direct reference was again made to the habitat. In Nicholson and Lydekker's Manual of Paleontology (196) we find the statement that "the nature of the deposits in which the remains of the Eurypterids are found, and of the fossils associated with them, would prove that these animals were essentially marine, their habits, probably being very similar to those of the existing King-crabs. It is, however, possible that certain of the Eurypterids were inhabitants of brackish or even of purely fresh waters" (196, 544).
In 1893, Malcolm Laurie, studying the eurypterid remains in the "Upper Silurian" of Scotland, i.e. the Siluric as generally used in America, found in those rocks of the Pentland Hills only one other fossil, Dictyocaris ramsayi, a crustacean (?) (144). The large eyes in most of the eurypterids which he found caused him to think that they must in some way be due to the conditions under which the creatures lived, and from a comparison with recent forms he was led to believe that the eurypterids lived in deep water, whether marine or not he does not say, but the former seems to be implied.
Amadeus W. Grabau writing in 1898 of the eurypterids said: "these crustacea were undoubtedly marine" (81, 362) thus accepting the usual classification and also the current opinion as to the habitat. On the other hand, Frech (70) at about the same time, said that the most evident proof of the retreat of the sea in the formation of the Old Red sandstone in England was the appearance in the Devonic of the eurypterids from the Baltic. This marks the beginning of the change in ideas and embodies the first statement contrary to the prevailing opinion that the habitat of the eurypterids was marine.
The period during which it was either tacitly assumed or definitely stated that these extinct merostomes had lived in the sea was thus brought to a close. There had been a few hints of a possible non-marine existence, but on the whole geologists and palaeontologists had for eighty years been agreed upon the marine habitat.
With the beginning of the new century we find a radical and sudden change of opinion. Chamberlin in his paper on "The Habitat
