Page:The Habitat of the Eurypterida.djvu/67

 marine, Grabau in favor of the non-marine. The Waterlime formation was particularly under discussion, but though many arguments were brought up on both sides, neither was able to convince the other.

In the June number of the Bulletin of the Geological Society of America (1911) Clarke writing, on the "Relation of the Palaeozoic Arthropods to the Strand-Line," speaks of the size of the eyes of eurypterids and crustaceans as indications of the depth of water in which the forms lived. It was formerly supposed that crustaceans with large eyes had acquired them by adaptation to great depth of water. Clarke cites the case of a trilobite with enormous compound eyes living among many Cambric forms wholly devoid of lenses, and other examples of a contradictory character, so that the size of the eye cannot be taken as proof of either deep or shallow water, but rather implies that the complex, highly-specialized eyes of certain forms enables these individuals better to adapt themselves to either deep or shallow water conditions. Clarke reiterates the opinion that "the few early eurypterids we know were doubtless marine, and the creatures gradually acquired the brackish-water habit of their climax, which seems to have eventually changed to a fresh-water life" (37, 280).

In 1912 the most recent contribution to the study of North American eurypterids was made in Clarke and Ruedemann's Monograph on the Eurypterida of New York (39). While the work has to do mainly with the description of species and the study of larval stages and of the anatomy, leading to fuller knowledge of the ontogeny and phylogeny of the eurypterids as well as their taxonomic relations, still the authors have given some attention to the question of the bionomy (39, 96–113), coming to the following conclusions:

"Summarizing these data we conclude that the eurypterids lived in the sea from Cambric to Siluric time. They had then become less sensitive to changes, positive and negative, in the salinity of the water. In fact they seem to have thrived best under conditions of life that excluded most other marine groups of animals, that is, in the marginal, more or less inclosed marine lagoons, accompanied by estuaries receiving delta-forming terrestrial drainage, with prevailing arid or sub-arid climate, the waters being in some places more than normally briny, in others having less than normal salinity. In other words they were euryhaline or able to live in both salt and brackish water.