Page:The Eurypterida of New York Volume 1.pdf/191

 of the body. Its surface was evenly and highly convex, culminating near the center at the ocellar mound. It is surrounded by a narrow thickened filiform border. The posterior margin is straight transverse with a faint indication of fulcra near the acute genal angles.

The compound eyes are subcentral in position, situated as stated in the preliminary description; the visual surface is crescentic and only prominent in compressed specimens, while the entire ocular node, which has the form of a sector, being rounded at the outside and angular on the inner side, is distinct only in young individuals. The eyes occupy about one third the length of the carapace. The ocelli are situated on a line connecting the centers of the compound eyes and located on a large, prominent mound.

Abdomen. The abdomen is slender, widening so little from the base of the carapace to the third segment that in many specimens it tapers with apparent regularity toward the telson. The length is three times the greatest width.

The preabdomen is widest at the third and fourth tergites. Its length is to its width as 5 : 4. The tergites are narrow bands with straight or but slightly curved transverse margins and parallel lateral margins. The anterior and posterior margins diverge near the lateral extremities where the segments widen somewhat. Their antelateral angles are produced into broad blunt lobes, while the postlateral angles are either rectangular or furnished with short acute lobes, that are directed posteriorly and increase somewhat in size in the posterior segments. The segments were originally highly arched with a narrow flat strip, representing the epimera, along the lateral margins. Each tergite was not only strongly bent from one side to the other but also from forward backward and highest in the anterior third, with a steep decline forward and a more gradual one backward, finally grading into a narrow flat border.