1090 NEW YORK STATE MUSEUM 



the pincers are edentate and the walking limbs carry light, claw- 

 like spines. 



The epistoma, instead of parting on either side from the 

 doublure by stress of compression or in molting, as an epistoma 

 of Pterygotus figured by Laurie (9) did, is seen to have divided 

 through the center, an occurrence observed in a large number 

 of specimens. Schmidt (12) figures an epistoma of Pt. osil- 

 i e n s i s Schmidt, which, while showing a tendency to divide 

 along sutures at the sides, has also a deep open cleft in the 

 posterior edge. It is evident that there is considerable varia- 

 tion in this plate in different species. 



The last of the differences lies in the telson, which is slen- 

 derly lanceolate and much longer than that o£ any known 

 species of Pterygotus. 



Regarding its resemblance to Eurypterus, it might be said 

 that, but for the marginal position of the eyes and relatively 

 large chelae, this form would easily be mistaken for a species 

 of that genus. The semielliptic form of the head and the slight 

 expansion of the swimming arms, recall E. lanceolatus 

 Salter (8), and . the slender telson gives the posterior part of 

 the body of a general Eurypteruslike appearance, hightened by 

 the spiniferous character of the walking legs and the short, 

 edentulous, masticatory preoral appendages. 



However, the walking legs are less robust. They consist uni- 

 formly of seven joints and are equally spiniferous, while in 

 Eurypterus, with the exception of. the first pair, there are more 

 than seven, and the fourth pair carries merely the three end 

 spines. In the preoral appendages, the basal joints, instead of 

 being flat expansions on which the pincers are articulated (15), 

 are segments a little longer than the pincers, which, in their 

 normal position, instead of hanging down over the mouth, do 

 not quite reach its anterior end. These pincers have been seen 

 in Eurypterus only in the Russian species E. f i s c h e r i . The 

 limbs of the sixth pair are less expanded at the ends than is 

 usual in Eurypterus, and have narrow, upright, instead of 

 heavy, subquadrate gnathobases. The operculum is simpler, 

 lacking the faint transverse suture and two subtriangular 



