Page:The Eurypterida of New York Volume 1.pdf/79

 the bilobed form of telson is its greater efficiency as a swimming organ." The general form of the body, notably the relatively small carapace which lacks the shoveling rim of other eurypterids, the slender body with relatively narrow preabdomen that gradually tapers into the postabdomen, are clearly adapted to greater agility, and the long slender prehensile pincers in front, show that Pterygotus was highly predaceous and not a burrower after worms as Limulus or a carrion eater as most of the crabs, which use their stout claws largely as organs of defense and for tearing pieces off their food. The poorly developed walking legs of Pterygotus attest that it was a bad walker or crawler. There, then, seems to remain by exclusion the single inference that Pterygotus was essentially a swimming creature, probably slow and therefore in need of the long prehensile pincers. The large size attained by some species (5 feet and more) would also indicate that they could hardly have been of burrowing habit.

Hughmilleria, in both its species, has a distinctly fishlike appearance in dorsal aspect, which is evidence of its agility; this is effected by the relatively long, convex, anteriorly angular carapace and the very slender form of the body, which gradually tapers to the stout tail spine. It also lacks the distinct shoveling edge of the carapace. Hughmilleria has much better developed walking legs than Pterygotus and lacks the broadening of the telson. As it is clearly a more primitive and less specialized form than Pterygotus, it is equally adapted to a crawling and swimming habit. Its telson was probably used as an organ of defense.

Slimonia, specialized in the position of its compound eyes at the anterior angles of the carapace, the broadened telson and slender form of body, seems adapted to swimming and by its well developed walking legs also to crawling.

All these three genera, in comparison with Eusarcus and Eurypterus, have relatively small and narrow swimming legs, which is the more