78 NEW YORK STATE MUSEUM 
prising as for the rest of their organization they appear to be better adapted 
to swimming than the others. Quite likely the more slender body required 
less effort and smaller organs to paddle it. 
In the group represented by Eusarcus, the carapace is subtriangular, 
raised in front, where it bears the marginal compound eyes, the walking 
legs are powerful and provided with long spines, the preabdomen is very 
broad and flat, the tail long and scorpionlike, with a curved spine that 
could be raised above the body as an organ of defense. This is a quite 
aberrant and highly specialized genus and doubtless its habits were different 
from those of the other genera. On account of its general form it is highly 
improbable that it was a good swimmer, in spite of the marginal, frontal 
eyes, and its scorpioid form indicates that it was given principally to 
crawling, scorpionlike, on the bottom and, as we have little doubt, 
to burying itself in the mud, with the eyes on the raised frontal end and 
the scorpioid tail projecting from the mud. It is a singular character of 
Eusarcus that the second pair of walking legs is longer than the rest, and the 
series decreases in posterior direction. This arrangement not only served 
to raise the eye-bearing frontal end of the carapace above the mud, but the 
long spiniferous legs in front undoubtedly aided also in seizing and holding 
the prey, the chelicerae being relatively small. 
The swimming legs of Eusarcus are relatively large and heavy, 
the segments carrying the blade being short and stout. The legs were 
therefore more strong than agile and quite surely adapted to digging and 
anchoring the creature in the mud. 
The group represented by Eurypterus and Dolichopterus is character- 
ized by the prevailing broad carapace with dorsal eyes, broad to slender 
body, relatively strong swimming legs and a spiniform telson. The stout 
walking legs in all members of this group leave no doubt that they 
were able crawlers on the bottom, but there is considerable evidence 
to show that they burrowed in the mud and were also well able to swim; 
some species more given to one, some to the other habit. The evidence of 
a burrowing habit is seen in the relatively broad carapace with a distinct 
