Page:The Eurypterida of New York Volume 1.pdf/345

 either side. Its distal end is reentrant and fused to the posterior part. This part is a little narrower, slightly tapering and beveled in from either side for one fourth the breadth, to the sides of a slightly raised platform which is flat-topped for the greater part of its length, but becomes concave posteriorly, forming a shallow groove at the abrupt end. The terminal angles are noticeably truncated. The appendage carried by the second sternite is partially covered by that of the operculum. It is very slender, its greatest breadth not exceeding one sixth the length. The anterior half is sublanceolate with a triangular base; the posterior is attenuate and terminates just within the end of the cleft. In the male the appendage is simpler and confined to the operculum, the following sternite being entire. It is wider and somewhat shorter than that of the female, the average length being only about two and one half times the breadth. It is convex, broadly lanceolate and slightly produced at the posterior free end which just clears the edge of the operculum. A specimen in which a portion of this organ is scaled away gives a cast of the interior showing small elevated lines radiating from near the center backward, and may possibly represent part of the vascular, or duct system of this organ. The two sexes are about equally represented in numbers.

The whole surface of the body is covered with imbricating, crescentlike or angular scales, sometimes carrying smaller ones of the same pattern. These scales are so minute on certain areas as to appear almost obsolete. They are most conspicuous on the ventral side of the preabdomen and appendages. On the cephalothorax and abdomen the scales point backward, on the paired appendages toward the distal end, and on the epistoma, forward.

This singular creature has the appearance of an Eurypterus with the carapace of a Pterygotus. The Pterygotuslike aspect of the carapace is principally due to the marginal position of the compound eyes.

Another character worthy of mention is the ornamentation, which consists of flat, imbricating scales that are crescentlike near the anterior margin and become angular posteriorly. They are evenly distributed over the entire body, carapace [pl. 60, figs. 6, 8], endognathites, metastoma, operculum and its appendages, save the telson where they have not been observed. On the distal segments of the endognathites they appear as small tubercles.