of the carapace. The position of the longer row of spines, however, will determine the side on which the walking legs come to rest when limply sinking to the bottom.
The difference in the walking legs finds its strongest expression in the fourth pair. In Eurypterus the fourth is not only longer and thinner than the others, but also lacks the spines, while in Eusarcus, it is the shortest leg of the last three pairs, though equally strong and, like the others, provided with spines on all segments.
Another difference consists in the form of the swimming legs. Corresponding to the plumper, heavier form of Eusarcus, these legs are more powerfully developed. The paddles are much longer and broader, while the preceding segments, connecting with the coxae, are much shortened and thickened, so that the eighth segment in Eusarcus is fully as long or even longer (in old individuals) than the 2–6 segments together. The latter segments are consequently, in their proportions and even in their form, entirely different from those of Eurypterus. In these characters the swimming leg of Eusarcus has become closely like that of larger species of Pterygotus such as P. buffaloensis.
Eusarcus scorpionis Grote & Pitt
Eusarcus scorpionis Grote & Pitt. Buffalo Soc. Nat. Sci. Bul. 1875. 3:1, pl. 1
Eusarcus grandis Grote & Pitt. Ibid. p. 17
Eusarcus scorpionis Pohlman. Ibid. 1881. 4:21
Eurypterus scorpionis Semper. Beitr. z. Pal. u. Geol. Oesterr.-Ung. u. d. Orients. 1898. 11:86 et seq.
Eurypterus scorpionis Seeman. id. 1906. 19:57
Not Eurypterus scorpionis Pohlman. op. cit. 1886. 5:29–30, pl. 3, fig. 3
Our description of this hitherto very imperfectly known species is based on the remains of 20 specimens, apparently all that have been thus far secured. Seven of these are entire, or nearly entire, specimens and one
