Eurypterus lacustris Hall var. pachychirus Hall
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 endognathites 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 extended 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 narrowing 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 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 somewhat 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-
