A CERA TA—MER O STOMA TA . 409 



19. E. dekayi Hall. Siluric. 

 Body proportionately short, with broad, short carapace; an- 

 terior part of abdomen very broad, with posterior part very much 

 contracted; next to last segment with lateral flanges. 



Occasionally in the waterlime at North Buffalo, New York. 



20. E. mansfieldi Hall. Carbonic. 

 Cephalothorax sloping forward and abruptly rounded anteriorly ; 



eyes reniform, with two broad, rounded elevations between; ab- 



FlG. 1 7 10. Eurypterus robustus^ under side of two individuals, X ] 

 (Pal. N. Y., III.) 



domen gently increasing to fourth segment then decreasing to 

 seventh, then abruptly narrowing at the eighth, which is about 

 half as wide as the fourth; sixth and seventh somites with acute, 

 produced lateral angles; five posterior ones with strong, angular 

 ventral spines ; telson long, narrow, extremely acuminate ; length 

 228 mm., greatest width 53 mm. 



Alleghany series of Pennsylvania, etc. 



IX. EusARCUS Grote and Pitt. 



Eurypterids with the six anterior abdominal segments greatly 

 expanded and the succeeding ones abruptly contracted ; the ter- 

 minal joint of the sixth pair of legs not expanded. Siluric. 



