Appendix 3 



NOTES ON PALEOZOIC CEUSTACEANS 



BY JOHN M. CliAKKE 



I THE GENUS PSEUDONISCUS 



IN THE EURYPTERTJS BEDS BELOW AND ABOVE THE GYPSUM 



AND SAIiT BEDS OF THE SALINA STAGE IN NEW YORK 



PLATEIS 1, 2 



One of the most notable events in the record of paleozoic time 

 was the cometary outburst of the great crawfish known as 

 Pterygotus, Eurypterus, etc. along the low coasts 

 and in the salt shore pools of the closing epoch of the Siluric. 

 In the great area of Siluric rocks of northern Europe and in 

 northern United States, from western Russia and the Baltic 

 Isles of Oesel and Gothland, through Britain to New York,. 

 into Ontario, Ohio, and Indiana, these curious creatures with 

 their peculiar attendant fauna have manifested thercuselves in 

 culminating development at the same horizon in the succession 

 of sediments. It was, I believe, the distinguished Russian 

 academician, Dr Friedrich Schmidt, who laid special emphasis 

 on this phase of Siluric faunas as a proper index of the close of 

 that era, accompanied, as these bizarre crawfish were, by 

 physical changes theretofore unusual to the historical record. 

 This suggestion was strongly supported by the opinions of 

 Murchison as expressed in the last edition of his Siluria, 

 For many years the common species of Eurypterus occur- 

 ring in the waterlimes of Herkimer county, N. Y., and described 

 therefrom as long ago as 1829 (DeKay), was regarded by Russian 

 geologists as the same as that abounding in profusion and most 

 beautiful preservation in the waterlimes and dolomites of the 

 island of Oeeel; and, though the identity of these forms is not 

 generally conceded, yet the similarity in these distant species is 

 so extremely close that their assumed independence hardly 

 bears the test of close analysis. It is now therefore a matter of 

 somewhat more than ordinary interest to record in the New York 

 faunas the presence of another of these merostome crustaceans 

 whose existence has heretofore been known only in the island 



