Page:The Eurypterida of New York Volume 1.pdf/192

 The first tergite is considerably shorter than the others. It is six to seven times as wide as long; the following ones are about four times as wide as long.

The sternites are less straight bands than the tergites, their middle portion curving forward more distinctly. Their antelateral angles are produced into broad rounded ears or lobes, while the postlateral angles are well rounded. The operculum has not been observed.

The postabdomen tapers uniformly to the posterior extremity which is but one third as wide as the anterior. The segments are all circular in section, and they gradually become longer while they diminish in width, the first segment being four times as wide as long, while in the last the width is to the length as 3 : 4. The segmental rings are very simple with but very inconspicuous lateral flanges in the first segments and none in the last.

The telson is bluntly lanceolate; at the base it is three times as wide as long. Its dorsal side is convex and raised into a median keel; the underside flat and the lateral margins are furnished with sharp, bladelike edges.

Appendages. In spite of the great number of heads found only the swimming legs have been observed In mature specimens [ pl. 21, fig. 11] these are remarkably short and protrude but little more than half the basal width of the carapace. The eighth segment (the palette) is long, elliptical, the ninth forming a small terminal claw. Of the seventh segment but a portion has been seen protruding from below the carapace and this indicates that it was considerably narrower than the following ones.

Ornamentation. No scales or tubercles have been made out on either the carapace or abdomen. The only traces of ornament observed are a median transverse line on both the sternites and tergites, with traces of more lines in the latter, especially near the anterior margin.

Ontogeny. In its ontogeny  includes a larval stage that is not only strikingly different from the mature but also highly suggestive phylogenetically by its great similarity to Strabops.