418 * 
PALAEONTOLOGY 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 striae 
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. 
Plate 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 macroplitlialums (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. 
