THE EURYPTERIDA OF NEW YORK 77 
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 fishike appearance 
in dorsal aspect, which is evidence of its agility; this is effected by the rela- 
tively 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 an- 
terior 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 sur- 
1The authors above cited with regard to the habits of Limulus, have not 
emphasized the use made by that animal of the telson in defending itself. When 
buried in the shore sand, at low tide, in spawning time, the erected spine protrudes 
through the sand, and thereby causes much annoyance to waders. 
