ing new to the opinions already expressed by so many authors. "It is an oft observed phenomenon that groups originally nourishing in the sea are confined during their decline in fresh-water. Here this applies only to the Gigantostraca [Merostomata], while the Xiphosura which appear formerly to have lived mainly in inland seas, are, today, however, marine only" (269, 308).
During the year 1911 several papers on the Eurypterida appeared in America. Clarke still held to his former opinion that "the few eurypterids we know were doubtless marine, and the creatures gradually acquired the brackish-water habit at their climax, which seems to have eventually changed to a fresh-water life" (37, 280). Stuart Weller in his discussion of the nature of seas in which dolomites are formed, brings out several good points. "In such magnesian beds as are present in the Cayugan period of the Silurian [i.e., Middle and Upper Siluric] we find a most peculiar fauna, constituted almost wholly of the strange Eurypteroid Arthropods whose fossil remains are almost never found in association with typical marine faunas, but which are present in situations, such, for instance as the plant-bearing beds of the Pennsylvanian, which indicate that they musthave lived in non-marine waters. The stratigraphic association of these Cayugan, Eurypterus-bearing beds with beds of salt and gypsum at once suggests that the waters of the period were highly saline and perhaps shallow; but, so far as I am aware, there is no inherent characteristic of the fossil Eurypterus which can in any way suggest that it may not have been a truly marine organism, and our conclusion that it was not such an organism is drawn from the physical surroundings of the fossil itself, rather than that the physical conditions are what we believe them to be on account of some peculiarity of the fossil" (296, 228). This point is well made, and is worth while remembering, namely, that there is nothing in the physical characters of the eurypterids to indicate that they lived in non-marine any more than in marine waters, but from their surroundings the former habitat is suggested. Moreover, the interpretation of the physical conditions of that time has not been based upon speculations about the characters of the eurypterids; it was definite knowledge about the physical conditions that makes it possible to say what must have been the character of the habitat of the eurypterids.
At the Kingston Meeting of Eastern Geologists in the spring of 1910 there was a warm discussion about the eurypterid habitat, Ruedemann, Schuchert, Hartnagel and others arguing in favor of the
