Page:The Eurypterida of New York Volume 1.pdf/357

 individual, the lateral margins converge but slightly forward; the anterior angles formed by the projecting eyes and the anterior margin being well rounded. In mature carapaces the lateral and anterior margins are less rounded and more nearly straight, the lateral margins subparallel. The posterior edge is slightly incurved. The surface is very gently convex, and seems to have been originally rather uniformly, but very moderately, elevated with a slight depression along the medio-anterior margin of the compound eyes. The latter are subelliptic, very prominent, project beyond the margin of the carapace and are located at the antelateral angle of the cephalothorax. Their length is nearly one half that of the lateral margin of the cephalothorax; their distance from each other is distinctly less than the length of the eye. As more fully stated in the generic description, the compound eyes are entirely smooth in their exterior view, the facets becoming visible only when the exterior layer of the cornea has become split off or on an interior view. The facets are small and squarish in shape. The ocelli are borne on a small oblong or rhomboidal tumescence, situated in a line connecting the bases of the marginal eyes, and sometimes prolonged posteriorly in a crest. The ornamentation consists of an extremely fine granulation evenly distributed over the carapace, becoming coarse between the compound eyes.

A relatively narrow doublure surrounds with uniform width the frontal and lateral margins of the cephalothorax. The doublure at the base of this shield is three times as wide; it follows the entire posterior margin, thus making the doublure ring complete.

Abdomen. The abdomen widens to the third or fourth dorsal segments, where, in mature individuals, it seems to have been wider by one fourth than the base of the cephalothorax. From this point it tapers very gradually to the telson.

Preabdomen. The first of the six tergites is shorter by one half than the following ones. It is a narrow band, rather strongly curved fonvard in the middle portion and rounded at the ends. The following tergites are relatively broad, their length amounting to one third of their width.