418* PALEONTOLOGY OF NEW-YORK. 



distal end, and strongly incurved. It bears on its inner edge six strong 

 but unequal teeth, which preserve slight marks of longitudinal strise 

 visible under a lens. 

 On another part of the same stone there is an elongate striated surface, 

 partly the substance and partly an impression, which may have be- 

 longed to this chelate organ. 



The caudal segment, referred with doubt to this species, is about one 

 and a half inches long and two inches wide : the surface is ornamented 

 by small, pointed, imbricating, scale-like processes, which are distant from 

 each other, and the intermediate spaces granulose. • 



This ramus of the chelate appendage was the first unequivocal fragment of the 

 Genus Pterygotus that came under my notice from any American locality, having 

 been known to me since 1854. 



Plate lxxxiii b, fig. 4. The free ramus of the chelate appendage of this species. 



Platb lxxxiv, fig. 8. An articulation of the abdomen, which probably belongs to this 

 or to some other species of this genus. 



Geological position and locality. In the Waterlime group near Buffalo. 



Pterygotus macroplitlialinus ( n. s.). 



Plate LXXX A. Fig. 8 & 8 a. 



Carapace semielliptical, slightly concave behind ; length equal to three- 

 fourths the greatest breadth : cornea-lenses oval, marginal, and pro- 

 jecting beyond the outline of the carapace, concentrically striated. The 

 distance between the eyes is less than the length of the eye. A small 

 central longitudinally oblong tubercle lies in a line with the posterior 

 angles of the eyes, and nearer to the base than to the anterior margin 

 of the carapace. This small subcentral tubercle is marked on each side 

 by a small rounded eye-like spot, nearer to the posterior end of the 

 tubercle. 



Surface preserving no organic markings ; being merely a blackened 

 ground, with the granular texture of the stone. 



