Page:The Eurypterida of New York Volume 1.pdf/349

 posterior edge is very gently concave forward, nearly straight. The dorsal surface was uniformly and strongly convex, culminating between the lateral eyes and somewhat impending along the sides. A narrow flat border surrounds the lateral and frontal margins. The compound eyes are of medium size (one fourth to one fifth of length of carapace), intramarginal in position, separated from the margin by an interval nearly as wide as the eyes themselves. On account of the position of the eyes on the impending sides of the carapace, however, they appear in most compressed specimens to be marginal [pl. 64, fig. 13; pl. 65, figs. 1, 6, 9]. They are placed so far forward that they are distant only their own length from the foremost point of the carapace. The form of the ocular node resembles that of an elliptic sector, the outer margin being rounded and the inner margin angular or composed of two, frequently unequal radii, the anterior being the longer. The anterior end of the node is acute, the posterior rounded. The node is so slightly prominent that the eyes hardly project beyond the outline of the carapace. The visual surface is crescentlike with somewhat swollen extremities [pl. 65, fig. 10] and situated along the outer edge of the ocular node. The ocelli are distinct, separated by the length of their own diameter, and situated on a flat circular tumescence that lies on a line connecting the inner angles of the compound eyes.

Abdomen. The abdomen is slender, increases slightly in width to the fourth dorsal segment and then tapers very gradually to the telson. Its greatest width is about one fourth the length of the body.

Preabdomen. The tergites [pl. 66, figs. 6, 8, 11] are narrow, subrectangular bands with anterior and posterior margins straight or but slightly bent forward, three to four times as wide as long, save the first which is six and one half times wider than long, or in other words, is a very narrow band. The anterior edge of the latter is straight, the posterior gently concave. The antelateral angles are broadly rounded and produced forward and the postlateral angles slightly extended posteriorly so that both extremities of this segment are widened. In the following