Page:The Eurypterida of New York Volume 1.pdf/323

 posterior parts contracted. In the young specimen, the length is to the width as 7 : 8, in the ephebic example, as 8 : 9. It is widest in the middle portion and contracts again by about one seventh of its width toward the base. The doublure is about 3 mm wide in the type specimen and relatively wider in the young. It diminishes in width posteriorly and finally runs out. The margin of the carapace is bounded by a thickened border, behind which several parallel striae are observed. The eyes are somewhat indistinct in the specimens; they appear to have been large and consisted of almost circular visual surfaces surrounding circular prominences. The latter occupied one fifth of the length of the carapace, were situated on the anterior half and not quite twice their width asunder. The ocelli have not been seen. The preabdomen is relatively very short (its length amounting to only two thirds that of the carapace) and broad (proportion of length to width as 4 : 5), its greatest width being attained in the region of the fourth tergite whence it contracts rather rapidly. At the widest part of the preabdomen, the tergites seem to be about six and one half times as wide as long. Their general form is but indistinctly discernible in the carbonaceous film, but seems to have been that of straight transverse bands. The operculum is not appreciably wider than the other sternites and the next sternite fully as wide. The details of the outlines of these and the following sternites have not been made out. The third sternite (the widest) is, in its exposed or not overlapping part, eight times as wide as long. The posterior margins are uniformly concave, the curvature increasing in the succeeding segments. The median suture is well seen in a young specimen [pl. 25, fig. 3]. The postabdomen shows an immense development; it is nearly as long as the carapace and preabdomen together and occupies about one third of the total length of the body. The first postabdominal segment still corresponds in anterior width to the preabdomen, but it contracts so rapidly that its posterior margin is shorter by one fifth and the final width of the postabdomen is but one third of that at its beginning. While thus the postabdominal segments diminish greatly in width posteriorly, they increase