416* PALAEONTOLOGY OF NEW- YORK. 



Genus Pterygotls (Aqassiz). 



This genus was established by Prof. Agassiz in 1844, in his "Monographic 

 des poissons fossiles du vieux gres rouge". The specimens then known 

 were all fragmentary ; and although some additional facts were from time 

 to time obtained, it was not until 1856 that Mr. Salter published* an 

 illustration of the restored form of the animal, under the name Himan- 

 topterus, which he subsequently determined to be identical with Ptery- 

 gotus. 



The form is very similar to Eurypterus ; the eyes being marginal in- 

 stead of within the carapace, while the caudal extremity is bilobatef . 

 The number of segments of the body, as represented, is one less than in 

 Eurypterus ; but this may have arisen from observing the lower side only, 

 and the suture, if existing as in Eurypterus, may not have indicated a 

 separate articulation. One other remarkable difference between this genus 

 and Eurypterus is in the "chelate antenna" placed at the anterior part of 

 the carapace ; a relation which seems scarcely credible, but for the au- 

 thority under which it is presented. 



A fragment, the free ramus of one of the chelate antenn£B| of a species 

 of this genus, has been found near Buffalo by Mr. Cobb j and in the same 

 collection with it there is a single joint, apparently a caudal joint, which 

 differs from any similar part of Eurypterus known to me at this time. 



• On some new Crustacea from the uppermost Silurian rocks, by J. W. Salteb, F.G.S.; with a Note on 

 the structure and affinities of Himantopterut , by T. II.Huxiet, F.G.S. ( Quarterly Journal of the Geo- 

 logical Society, Vol. xii, p. 26.) 



t The spiniform caudal appendages, figured on the same page as belonging to this genus, may prove to 

 be Eurypterut. 



t Chelate antennae of Hcxlkt and Salter. Notwithstanding that these organs are placed at the anterior 

 part of the carapace, and in the position of antenna;, the similarity of structure in Pterygotus and Eury- 

 pttrut induces me to believe that other relations of these parts will yet be found; and that chelate an- 

 tenna: of this character, and in this position, do not belong to Pterygotus ; or else that we have misunder- 

 stood the specimens referred to this genus among our collections. The many structural analogies between 

 these crustaceans and Limulut would induce me to regard these organs as analogous in some measure with 

 the chelate antenns [palpi] of that animal, and as having a similar position anterior to the mouth. 



