Page:The Eurypterida of New York Volume 1.pdf/171

 described by Holm [ text fig. 32] has not been seen in our material, probably because, as in Limulus, only the mature individuals after the last molt possessed it. Besides the long paired spines, each segment was furnished with one or more short, blunt spines [ pl. 7, fig. 2], located at the anterior margin. The clawlike terminal segment and the spines of the penultimate segments are shorter than the others. As in most Eurypteri, the fourth endognathite lacks the spines, except those of the last two segments, and is relatively longer and more slender. As none of the coxal segments of the first three pairs of endognathites have been found detached, we are unable to describe them beyond stating that they are short and broad and bear at the inner upper angles, dentate manducatory faces with short conical teeth. They apparently show the progressive changes in form posteriorly as described by Holm. The coxa of the fourth endognathite is seen on plate 7, figure 6. Its length and width are nearly equal, while in the preceding coxae the width surpasses the length. The manducatory edge is borne on a marked prolongation. The circular foramen of the posterior margin, to which an auditory function has been ascribed, is well shown. Plate 4, figure 2, shows the mode in which the coxae of the endognathites are arranged like the tiles of a roof, exposing in ventral view only the upper margin and the prolongation bearing the manducatory edges, while plate 4, figures 2, 3, show the relative length and thickness of the endognathites.

The swimming legs are strongly developed in this type. When reflexed, they reached to the sixth tergite, and are correspondingly stout. The coxa is usually well exposed [ pl. 6, fig. 8; pl. 7, fig. 7, 8]. It is subquadrate, broader in front than behind; the manducatory face is about one third the length of the inner margin and borne on a well defined neck. The face consists of a beveled chisel-like upper half followed by a more prominent row of six to seven denticles that are shorter than those of the other legs [ pl. 7, fig. 6]. The second and third joints are short and ringlike. The stemlike process by which the second joint articulates with the coxa is distinctly seen in plate 7, figures 7, 8. The fourth segment is about one