THE EURYPTERIDA OF NEW YORK 285 
spines or bristles well adapted to broaden the swimming surface of the limbs. 
To the first leg of S. excelsior which is the only one observed, paired 
flat spines are attached whose form suggests their adaptation to swim- 
ming. We are disposed to regard all legs as adapted for crawling. Though 
in some species the forelegs served as swimming organs, the long posterior 
ones were mainly active in pushing the animal forward. 
In another group of species again the forelegs do not differ in relative 
length and character from the walking legs of Eurypterus. The typical 
representative of this group is S. logani. This leads us to the dis- 
cussion of the subdivisions of Stylonurus, distinguishable on the basis of 
leg structure. On comparing the figuresof S. logani and 5. mac- 
rophthalmus [text fig. 65] with those of 5. cestrotus and 
S. elegans, it is at once evident that in the former the forelegs 
are not only relatively smaller and narrower than in the other but are also 
provided with only one pair of spines each, as in Eurypterus, while in the 
latter group these legs are relatively much longer, more powerful and 
furnished with a contiguous series of long spines, each segment carrying a 
greater number of spines than two, a character apparently not repeated 
in other genera.'! A third group is represented by 58. scoticus Wood- 
ward. In this, the single limb known (obviously one of the last pair) is 
greatly broadened from the beginning and is distinctly a swimming leg. 
The similarity of this swimming leg to that of Eurypterus would suggest 
a reference to the latter genus if the other characters of the animal 
were not so manifestly stylonuroid. Still the species is not a typical Styl- 
onurus but distinctly a later and more specialized form. This is shown 
not only by the swimming leg but also by the large hooked, winglike epi- 
mera of the postabdomen and the sculpture of the tergites. It demands 
recognition as representing a subdivision of Stylonurus. 
1 Laurie’s figure of Eur ypterus scoticus [1899, pl. 39, fig. 26] shows on 
the fourth segment three spines, which would suggest a like feature, but since the suc- 
ceeding segments clearly possess only two spines it would seem that this appearance 
of a close series of spines is accidental. | 
