228 • NEW YORK STATE MUSEUM 



known; longitudinally grooved; periodic depressions or large pits 

 in the grooves; shown as blunt spines on the rock mold. 



^ 



Fig. 160 Ceratiocaris (Phasganocaris ? ) deweyi. Telson (reduced) 



Found in the Lockport limestone at Niagara; also in the shale at 

 Lockport (Hall). 



Order jsuryf-tk^ridj!.^ Burmeister 



The eurypterids are large Crustacea, with an elongate body com- 

 posed of cephalothorax, a ringed abdomen, and a tail piece or telson. 

 The body is covered by a' chitinous epidermal skeleton, and could 

 be cast off as in the modern horseshoe crab (Limulus). The 

 cephalothorax is usually furnished dorsally with two large, facetted 

 lateral eyes, and a pair of median ocelli; and ventrally with six pairs 

 of legs. The anterior joints or rings of the abdomen bear on their 

 under side five pairs of broad, leaf-like appendages, which are com- 

 parable to the gills and operculum of the horseshoe crab. The 

 posterior six segments are without appendages. The legs are com- 

 parable to those of Limulus and, like them, their inner margins are 

 furnished with stout spines which serve as teeth. The last pair of 

 legs is generally large, and usually somewhat flattened, and ends in 

 an oval plate. This *' paddle " may have been used for swimming 

 purposes or for purposes of anchoring. On the under or ventral 

 surfaces of the first two abdominal segments is the genital oper- 

 culum, a pair of plates meeting medially, with a median lobe at- 

 tached which differs in the two sexes. 



Genus eurypterus DeKay 

 [Ety.: eof^u^, broad; r.refxh, wing] 



(1825. Lye. nat. hist. N. Y. An. 1:375) 



Body elongate and narrow, often of great size. Cephalothorax 

 one fifth or one sixth of the whole length, depressed convex, of a 

 subquadrate outline with the anterior angles rounded, and the pos- 

 terior margin slightly concave; entire margin bordered by a narrow 

 marginal furrow. Eyes reniform, situated somewhat in front of the 

 middle; ocelli close to the axial line. Mouth a ventral cleft. Legs 



