80 NEW YORK STATE MUSEUM 
awaiting their prey or digging for it as Limulus does. A good instance 
of such a species is E. pittsfordensis. 
We consider the genus Dolichopterus well adapted to a swim- 
ming habit. This is indicated by the notably forward position of the 
compound eyes and the remarkable lengthening and broadening of the 
swimming legs. The lengthening has been produced not only by the 
great lengthening of the segments, but also by the development of the ninth 
segment (only a minute claw in Eurypterus), into a palettelike plate. We 
have also shown [see generic description p. 264] that the spines on the swim- 
ming legs are transformed into expanded leaflike appendages, which serve 
to broaden the limb. If these appendages were arranged in whorls, as in 
Limulus, the claim could be made that they served in digging as in the 
latter genus, but it is difficult to conceive that these appendages, arranged 
in a series on the posterior side of the limb, could have well served that 
purpose, since they would fail to push the mud.outward as does the leg 
of Limulus, but would move it backward and inward. Nor is the great 
length of the swimming legs favorable to the digging function, for digging 
organs are always short and stout; and as for serving only as anchors in 
the mud it would not seem necessary to lengthen the limbs to such extent. 
The last group, represented by Drepanopterus and Stylonurus, shows 
again a different adaptation. Here the legs exhibit a distinct tendency 
to become greatly lengthened without being broadened. It is obvious that 
these forms were not mud dwellers, and if we consider Drepanopterus as: 
the ancestor of Stylonurus, they were originally crawlers. 
Drepanopterus [see restoration pl. 54] possesses five pairs of walking 
legs which increase regularly in length backward and exhibit no differen- 
tiation, except that the frontal legs have longer spines and the last pair is 
spineless. The very broad shovellike carapace with its elevated eyes and 
the long styliform telson are, however, quite suggestive of a mud-grubbing 
mode of feeding. 
In Stylonurus the tendency of Drepanopterus to lengthen the last 
pairs of legs has reached its extreme. While all its species exhibit these 
