Page:The Eurypterida of New York Volume 1.pdf/169

 [ pl. 5, fig. 5], the marginal portions but slightly flatter than the rest; in many partly compressed specimens [ pl. 4, fig. 4] the axial part remains prominent, as in the axis of the trilobites, while the lateral parts assume an aspect similar to that of the pleura. They are depressed and slightly raised toward the margin and bent specimens show on the inner side folds that are slightly curved and pass obliquely forward. The first tergite is narrower than the others and its postlateral angles truncated like those of the carapace. Its length is about seven and one half times the width. The middle portion of the tergites is broadly arched forward, while the lateral portions are normal to the axis of the body or again curve forward. The antelateral angles are produced into articulating lobes. The tergites overlap along their anterior margins about one sixth their length. The posterior doublure is about one fifth the length of the segment. The ventral side of the preabdomen appears to have been more convex than the dorsal, for in compressed specimens the edges of the ventral plates project on both sides beyond the dorsal plates [ pl. 4, fig. 4]. Probably the ventral median line was somewhat depressed, as in. The five sternites are longer than the tergites, medially cleft, bounded by straight transverse anterior and posterior margins and, with the exception of the operculum, are furnished with large rounded antelateral lobes. The operculum is longer than the other sternites, its antelateral angles are rounded off, while the anterior edge is produced into a broad median lobe. A like lobe is observed on the second sternite in the female. The postmedian angles of the two opercular plates are also produced into lobes, while those of the following sternites are well rounded.

The postabdomen is one third as long as the whole body. From the first to the sixth segment the width decreases by three fifths of the width of the first segment, while the length of the last is double that of the first. The first differs in appearance from the others in having the lateral margins strongly convergent backward, thus resembling the preceding tergites, while the others have subparallel lateral margins. Likewise the first segment has broadly convex anterior and equally concave posterior