64 THE HABITAT OF THE EURYPTEREDA 



CHAPTER III 



The Bionomy of the Eurypterid Faunas 



introduction 



In the first chapter I confined myself to facts which consisted of 

 observations made in the field or the laboratory by students of the 

 rocks and of the faunas. Such facts covered data on the geological 

 and geographical distribution of the eurypterids; in the second chap- 

 ter I gave a resume of the opinions which have been held by various 

 writers in regard to the habitat of the eurypterids; the remainder of 

 the paper will be devoted to the contemplation of the recorded facts 

 whose interpretation will be undertaken in the light of principles 

 recognized by the school of philosophical geologists. For this reason, 

 I shall in nearly all cases use the deductive method of inquiry, estab- 

 lishing the general principles which may then be applied to the par- 

 ticular case in hand. It is evident, then, that before we can begin 

 to adduce proofs r avoring one mode of life or another for the euryp- 

 terids, we must have a good classification of habitats in which each 

 type is clearly defined, and we must determine at the very outset 

 whether there are any criteria which may be recognized in the rocks 

 as absolutely diagnostic of the habitats of the past. In so far as de- 

 posits in the sea and on the land have received any consideration at 

 all, distinctions have mainly been drawn on the physical character ; 

 of the sediments; but I believe that much more accurate and far 

 reaching results are to be obtained from the study of the fossil faunas. 

 These may be investigated from two points of view, either the choro- 

 logical, or the bionomic; and besides these, there is yet a third line of 

 approach, namely the geological, in which the physical characters and 

 lithogenesis of the sediments, together with the correlation of syn- 

 chronous deposits constitute the elements. These three lines of in- 

 vestigation deal with three, for the most part mutually independent 

 groups of facts and I am convinced that any one will yield sufficient 

 evidence to determine the nature of any past habitat. In this chap- 

 ter I shall deal with the bionomic characteristics of modern habitats, 

 and shall give the criteria for recognizing ancient ones, concluding 

 with the special case of the bionomy of the eurypterids. The fol- 

 lowing chapter will be devoted to the geological evidence regarding 

 the habitats, while I shall defer until the fifth chapter the chorological 

 evidence which is more conveniently discussed with the geological 



