THE EURYPTERIDA OF NEW YORK 259 
sure, although it remained monotypic until Holm referred two metastomas 
from the dolomitic shale of Rootzikiill, Island of Oesel,' to this genus. 
The Bertie waterlime of Williamsville, near Buffalo, which has furnished 
the genotype, has afforded the carapace of a second species, here de- 
scribed as D. siluriceps,and the shale of the Shawangunk grit 
at Otisville has furnished a third species which sheds much interesting light 
on this rare and little known genus. We have named this last species 
D. stylonuroides because the carapace has all the characteristics 
of that of Stylonurus [pl. 46, fig. 13] in its subrectangular outline, broad 
doublure with frontal triangular plate on the underside and broad rim of the 
dorsal side, position, relative size and form of the lateral eyes. Its most 
peculiar features are, however, its swimming feet which appear beset with 
leatlike plates, the last segment being tripartite and consisting of three lance- 
olate plates. It is not difficult to recognize in its structure a further 
development of the peculiar lobelike lengthening of the segments of the last 
pair of legs noticed in D. macrochirus and to see in the tripartite 
extremity of the leg the result of the strong development of the ninth 
segment characteristic of Dolichopterus, the middle lobe representing the 
ninth, the lateral ones the preceding eighth segment. The same development 
of lobes 1s shown on the preceding pair of legs in the genotype and the leg 
retained in D. stylonuroides still further resembles that balancing 
leg as the last segment is developed into a spine, flanked by two lobes. 
This interesting combination of a Stylonurus carapace and Dolichop- 
terus leg in the same specimen suggests the question of the relationship of 
these two genera. A comparison of the two shows that Dolichopterus 
is more closely related to Stylonurus than to Eurypterus as a subgenus of 
which it was regarded by Hall and with which it has been associated by 
later authors. The similarity in the outlines of the carapace 1s manifest; . 
they also have in common the distinctness and great width of rim, 
‘As we shall presently show, the metastomes of Stylonurus and Dolichopterus 
are alike or very similar and the two genera closely related. It is therefore possible 
that more complete material of the Oesel species will show them to belong to 
Stylonurus. 
