Page:The Eurypterida of New York Volume 1.pdf/233

 legs are in the same number as in Eurypterus. The swimming feet appear to differ by the straighter, less rounded outer margins. In the specimen the rhomboidal plates are not given. From the impressions of the joints of the swimming feet their relative dimension does not seem to accord with Eurypterus. The four pair of anterior feet proceed from two elongate oral plates of which the impression is very distinct. The spines of the anterior feet appear to be long, curved, and to have an anterior direction. The absence of chelate appendages to the posterior margin of the feet is particularly noticeable. The first seven broad segments of the abdomen form a large ellipse. There is an evident and remarkable narrowing of the succeeding caudal segments. Of these six appear to be made out on the specimen. The surface of the cast is punctate with scattered triangular impressions. The cast shows a widening of the terminal segment and no traces of a spiniform process are exhibited.

Of the differentials indicated in the passage quoted, the following have stood the test of larger collections: the much "narrower" cephalothoracic portion, the broad large ellipse of the abdomen and the "remarkable narrowing" of the postabdomen ("caudal segments"). At least three, possibly four species, exhibiting quite similar characters of general form, are known from the British Siluric rocks and these have been referred to Eurypterus by Woodward, the differences in outline not being considered of generic importance by that eminent authority. It is not surprising therefore that authors generally have shown little inclination to recognize this genus Eusarcus.

Grote's successor as curator of the Buffalo Society's museum, Mr Pohlman, was apparently the first to assail the proposed genus, stating [1886, p. 29] that the discovery of several new specimens had shown that the form has "the leading characteristics of the genus [Eurypterus], as given by DeKay," viz, "a terminal joint prolonged into a sublinear or lanceolate triangular spine with serrated edges," and "eyes reniform or oval, placed within the margin of the carapace." Pohlman's observations in regard to the telson, which is as in Eurypterus, are correct, but the original of the supposed carapace of Eusarcus which he figures [op. cit.