THE EURYPTERIDA OF NEW YORK 179 
Eurypterus lacustris Hall var. pachychirus Hall 
Plate 12, figure 3; plate 19, figure 1 
Eurypterus pachycheirus Hall. Palaeontology of New York. 1859. 1: 
412*, pl. 82, fig. 1-3 
This variety which Hall separated from E. lacustris is based 
on an abdomen, a group consisting of two swimming legs, several endo- 
gnathites with operculum; and a separate swimming leg. The types of the 
abdomen and the swimming leg are in the State Museum; the group 
of swimming legs and operculum in the American Museum of Natural 
History. The species is diagnosed as follows: ‘‘ Carapace unknown. 
Body robust: crust thick; articulations strong, those of the abdomen ex- 
tended in strong salient angles at the lateral edges. Bases of the anterior 
feet strong and broad. Swimming feet strong and large; the seventh 
(sixth) joint very large and long, inflated and much curved on the anterior 
side; the free eighth joint is thick and strong, somewhat oval, and narrow- 
ing gently toward the point of articulation; the terminal palette is small. 
The last joints (and perhaps the others) of the swimming feet are serrated 
on the margins.”’ 
In the notes it is added that “the peculiar arching of the seventh 
(sixth) joint, and the thickened or inflated character of the swimming foot 
in this species, appear to be sufficiently characteristic to rely upon for 
d) 
specific distinction,’’ and as further distinctive characters are mentioned, 
that the scaly surface marking of the body is more strongly developed 
than in any other species observed, and that the anterior margin of each 
segment is raised in a little elevated band, more prominent and more 
strongly serrate on its anterior edge than in any of the other species, and 
finally that the surface is marked by strong longitudinal wrinkles some- 
what irregularly disposed. | 
The. great width of the distal portion of the swimming leg and 
especially that of the seventh segment appear as good distinctive 
characters, when compared with the narrower appendages of the typi- 
