60 THE HABITAT OF THE EUKYPTERIDA 



ing new to the opinions already expressed by so many authors. "It 

 is an oft observed phenomenon that groups originally flourishing in 

 the sea are confined during their decline in fresh-water. Here this 

 applies only to the Gigantostraca [Merostomata], while the Xipho- 

 sura which appear formerly to have lived mainly in inland seas, are, 

 today, however, marine only" (269, 308). 



During the year 191 1 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 gradu- 

 ally 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 must have 

 lived in non-marine waters. The stratigraphic association of these 

 Cayugan, Eurypterus-b earing beds with beds of salt and gypsum at 

 once suggests that the waters 1 of the period were highly saline and 

 perhaps shallow; but, so far as I am aware, there is no inherent char- 

 acteristic of the fossil Eurypterus which can in any way suggest that 

 it may not have been a truly marine organism, and our conclusion 

 chat it was not such an organism is drawn from the physical sur- 

 roundings 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 re- 

 membering, 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 habi- 

 tat is suggested. Moreover, the interpretation of the physical con- 

 ditions 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 



