Page:The Eurypterida of New York Volume 1.pdf/203

 are comparatively short, the length averaging a little less than one fifth the breadth. They are broadly concave along the middle of their posterior edges, and each carries, bordering this curve, four raised, triangular scales like the two on the posterior border of the cephalothorax and the middle two in line with them. The five sternites are medially cleft and marked by transverse sutures, which give to each the appearance of having been formed by the fusion of two plates. With the exception of the first or operculum, they have the antelateral angles projected forward into small lobes. In the operculum these angles are noticeably rounded away, and the anterior edge is projected into a broad median lobe. In the female the second sternite has a similar lobe. The annulate segments, or sclerites, comprising the postabdomen increase in length and decrease in breadth from the first, which is very broad and short, to the last in which the length exceeds the width of the anterior or wider end. They are depressed and have faintly defined pleural areas or flattenings at the sides. Each is prolonged on either side, at the posterior angle, into a short, striated spur, which grows longer with each succeeding segment, those on the last forming conspicuous pointed lobes. The first two segments each carry on the dorsal side four triangular scales like those of the preabdomen, the third, fourth and probably the fifth, each two, the last none. This segment has a shallow notch in the middle of the dorsal, posterior edge, marked on either side by a small denticle, succeeded toward the sides by very minute ones. The series of striations of the lobes continue up the sides of the segment to its articulation with the preceding. On the ventral portion of each ring segment is a shallow posterior emargination fringed with lobelike teeth. Extending forward from near either end is a curved rent, a pair sometimes almost inclosing an irregular, oval area.

The telson is very long, nearly equaling in length the rest of the postabdomen. For a short distance from the anterior end it contracts rapidly, then continues slender to the abruptly rounded point. The edges are sharp and, from near the anterior end, are marked by short, oblique incisions. The dorsal surface is smoothly convex, the ventral has a flat topped carina which begins near the proximal end and extends to the tip. On the carina is a double row of pits like those bordering the cephalothorax.

The doublure, at its dehiscence in the axial line, equals in width about one fourth the length of the cephalothoracic shield. From this point it narrows toward the genal angles.

The preoral appendages have not been observed. The endognathites are robust and vary greatly in length, the first pair being barely long enough to reach the shield border, while the members of the third clear it by fully three fourths their length. The fourth pair is known only by a coxal joint and a basal portion consisting of three joints. The first legs consist of seven joints; the second and third each, of eight. In the first