194 THE HABITAT OP THE EURYPTERID A 



The eurypterid fauna of Condroz, Upper Devonic of Belgium. 



Pterygotus problematicus, occurrence doubtful in Aymestry 

 limestone. 



Eurypterus punctatus fragments, Wenlock limestone, England. 

 To the second belong: 



Strabops thacheri, Potosi limestone, Upper Cambric or Lower 

 Ordovicic. 



Eurypterus prominens, Clinton. 



E. boy Hi, Guelph. 



E. microphthalmus, Manlius; Monroe. 



Pterygotus problematicus, May Hill sandstone, Llandovery. 



Eurypterus sp. Wenlock (of Southern Belt, Scotland). 



Eurypterus sp. Wenlock (Girvan area, Scotland). 



Pterygotus australis. Upper Siluric of Australia (Informa- 

 tion insufficient, may belong to group i). 



Pterygotus osiliensis, Pterygotus marl of Gotland. 

 To the third group belong: 



The Siluric fauna of Bohemia. 



The Lockport fauna of Ontario. 



The Siluric fauna of Podolia and Galicia probably belongs here. 



Pterygotus sp. Siemiradzki, Middle Devonic of GalLia. 



The lines of argument for the above occurrences have been stated 

 from time to time, but are scattered throughout the paper. They 

 may be brought together here for reference since so many of the cases 

 are subject to the same arguments. In chapter III the criteria for 

 recognizing the various types of habitats in the past were fully dis- 

 cussed, and will now be of great help in establishing the nature of the 

 habitat indicated by the various eurypterid occurrences given in 

 the three lists above. In the light of the arguments that have 

 gone before, and especially of the discussion on habitats, the following 

 truths may be considered as self-evident or as easily demonstrable. 



i. The occurrence of a single fragment, or of two or three frag- 

 ments, or of a single complete eurypterid in a formation where it is 

 associated either intimately in the same stratum or closely in adjoin- 

 ing strata with a typical marine fauna, as defined on p. 76, cannot 

 be considered as proof that the eurypterid remains are a part of the 

 marine fauna, for the following reasons: (a) it is impossible to explain 

 how any group of marine organisms could have their remains so com- 

 pletely destroyed that but a single fragment should be left; such is 



