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 characterized 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
