the important members and appendages of the animal, the body is sufficiently well-preserved to distinguish the species, which is also characterized by the ornamentation of the joints of the swimming limbs. The occurrence of crustaceans of this character, in these rocks, is so rare that every specimen is of importance.
E. Pennsylvanicus is a smaller and more fragile form; they cannot be directly compared on account of the imperfection of the material.
Formation and locality. Chemung group; Warren, Pa.
Eurypterus Pennsylvanicus.
Plate V, Fig. 18.
Eurypterus Pennsylvanicus, C. E. Hall, Proc. Am. Phil. Soc.; Vol. VII, p. 621, 1877.
Carapace semi-circular; length a little more than half the breadth, post-lateral angles mucronate.
Eyes situated on the anterior half of the carapace, separated by a distance equal to about one-half the breadth of the head. Midway between the eyes is a small flat node or elevation, on each side of which is a larger longitudinal prominence. There are also two similar nodes above the posterior margin. The posterior angles show two oblique short ridges. These elevations of the carapace probably indicate the positions of internal organs and the points of attachment of muscles.
The surface ornaments are not well-preserved, the specimen shows numerous small tubercles, especially over the posterior portion.
The carapace has a length of 8.5 mm. and a breadth of 15 mm.
The shape of the carapace and the arrangement of the nodes is quite different from E. Mansfieldi, and the geological position is considerably higher in the series than E. Beecheri.
Formation and locality. In an arenaceous shale; at Rooker farm, Pithole City, Venango Co., Pa.
