Eurypterus dekayi Hall
Eurypterus dekayi Hall. Palaeontology of New York. 1859. 3: 411*, pl. 82, fig. 1
This species was based on a single specimen, now in the State Museum [pl. 20, fig. 1]. Its distinguishing characters are thus given in the original description: "The entire body is proportionally shorter, the carapace shorter and broader than in E. remipes. The swimming feet are shorter, and the terminal palette a little more developed than in E. remipes or E. lacustris, and the upper abdominal joints differ less from the thoracic joints in length, while the last one is alate on the two lateral edges, a feature not observed in any other species."
The aspect of the type is that of a specimen which has distinctly suffered contraction by a shoving together of the segments and, mindful of the strange changes in aspect resulting from a pushing or pulling of the segments, especially in cast-off integuments, one might reasonably infer that all the above cited differences, save the alate lateral edges of the last segment, were largely of casual origin. The other specimen figured on plate 19 which is more favorably preserved, exhibits the same and additional distinctive characters while it is clearly but partially contracted in the preabdominal region and distended in the postabdominal. The most striking new character in this specimen is the presence of four to five long spines on each segment of the endognathites, instead of but one or two in all other members of the genus. The combined evidence of the two specimens leaves no doubt that we have to regard E. dekayi a peculiar aberrant type of Eurypterus. The following are the characters of this species:
Description. Body of small size, short but broad and compact. The carapace is about one sixth the length of the body, the latter a little more than three times as long as wide.
