BUFFALO SOCIETY OF NATURAL SCIENCES 235 



p. 205 above. If we assume such a mode of distribution by rivers for 

 the eurypterids, it would explain the close relationship which exists 

 between forms isolated, but in neighboring localities; that is, Euryp- 

 terus lacustris of the Buffalo area, and E. remipes of the Herkimer area, 

 nearly related species, but occurring in two isolated localities. But 

 besides, these two occurrences, the river hypothesis must account 

 for the close relation of both of these species to the one in the Baltic 

 region (see below p. 235). There is good stratigraphic reason for 

 believing that in Siluric time there was a continental mass (the 

 Atlantica of Grabau), which as already outlined occupied much of 

 the present North Atlantic and extended from northern North 

 America entirely across to eastern Europe. According to Walther, 

 several high mountain chains extended across this land connection 

 (294, 251), and undoubtedly large rivers came down from these. 

 Their headwaters would very probably interlace, 'as do those of all 

 large rivers on the various continents at present. 



Under such conditions we can see that the common ancestor of 

 Eurypterus lacustris, E. remipes and E. fischeri could have lived in 

 the headwaters of one of those rivers, and that getting farther away 

 from the point of origin, the various species derived from it would be 

 differentiated. E. lacustris and E. remipes were developed in two 

 neighboring streams, but the forms connecting E. remipes and E. 

 fischeri which must have lived in the rivers of Atlantica, are now 

 buried under the waters of the North Atlantic Ocean. The more 

 distant relationship of these species suggests that there were inter- 

 mediate forms, though these have not yet been found, and are prob- 

 ably nowhere preserved, though it is not impossible that Siluric strata 

 with such intermediate species may exist beneath the ice cap of South- 

 ern Greenland. In this great system of rivers,. which to all appear- 

 ances characterized the continent of Atlantica, the Bertie and Herkimer 

 Rivers were not very far apart, so that the faunules of each were very 

 similar. In fact, the deltas spread out at the mouths of the two rivers 

 may have become confluent in their outermost or seaward portions, 

 though the water lime now known would, as above explained, repre- 

 sent only the inshore facies. It may have happened that in times of 

 flood the river waters flowed out over a broader area near the de- 

 bouchures until some of the distributaries became for a time con- 

 fluent, thus allowing some of the species from one river to be carried 

 over into the area of deposition of the other. Thus might the pres- 

 ence of Pterygotus cobbi in both regions be accounted for. 



