Page:The Eurypterida of New York Volume 1.pdf/343

 segments are plain, bandlike rings, decreasing in breadth backward. In the first the breadth is considerably greater than the length; in the last, or penultimate body segment the length and breadth, in compressed specimens, are equal. The anterior end of each of these segments is marked by a groove for the attachment of the interarticular membrane.

The telson is very slenderly lanceolate, widest near the anterior end and attenuated at the tip. In length it is equal to the four preceding segments. The dorsal surface is convex, rising from sharp, lateral edges to a median longitudinal carina, which begins in the anterior part as a broad, angular prominence; the ventral surface is nearly flat or faintly convex; a cross section is thus subtriangular. Compression usually flattens the sides and thus heightens the angular appearance. The uncompressed specimen has a length of 31 mm and a greatest breadth of 7 mm.

On the ventral surface of the cephalothorax, in front, is a convex lobe or platform, the epistoma, from which extends a flat, tapering doublure ending in a small expansion at the genal angles. In molting and also from compression, the epistoma divided through the middle rather than along the sides.

Appendages. The preoral appendages are short, stout, three-jointed, chelate organs attached at the posterior border of the epistoma. The two distal joints of each form a pair of broad based, edentulous, bevel-edge pincers, in the ordinary state of compression having a breadth equal to one half the length. The blades are about equal in length to the basal portion and meet at the very acute, slightly curved tips and again, usually, only near the base. There is considerable variation in the relative form of the pincers, as shown on plate 11. The broad basal joints are about one fourth longer than the pincers, widest near the base and longest on the inner side, and in the natural position extend beyond the anterior margin of the shield for about one third their length. The pincers articulate with this joint in such a way that, when folded backward, they cross it obliquely, and their tips converge a little in front of the mouth; when extended forward, they diverge somewhat. The preoral appendages could also be turned back to their full length over the mouth, the pincer tips then overlapping the metastoma. In an individual having a cephalothorax 22 mm long, the preoral appendages are 10 mm long.

The four pairs of endognathites, or crawling legs, do not differ materially from one another except in length. The anterior limbs are somewhat shorter than the extended preoral appendages, and their tips extend but very little beyond the margin of the shield. Each succeeding pair is about one half longer than the preceding, so that the last limbs are probably four times as long as the first. All have seven joints, of which the terminal is spiniform. The third to the sixth joints inclusive carry ventrally and at the distal ends a pair of striated, slightly curved, slender spines. The