20 



It appears that this is the first notice of the maxilliped of 

 Pterygotus from the American beds. The present discovery of 

 the maxilliped of Pterygotus in the Silurian, is an essential confir- 

 mation of the existence of the genus in North America. 



It is possible that the articulation of the abdomen, doubtfully 

 referred by Professor Hall to IHerygotus Cobbi, and figured by 

 him on plate 83 b., of the Palaeontology of the State of New 

 York, belongs to JEuscoxus, a genus which must be conceded to 

 be more nearly allied to Eurypterus than to I*terygotus. It is 

 also possible that the chelae figured as belonging to Eurypterus 

 pachycheir^is, belong likewise to Eusarcus. 



