Page:The Eurypterida of New York Volume 1.pdf/376

 was connected or gradually passed into the thin ventral integument of the cephalothorax. The inner margin of the frontal notch is thickened and a median thickening proceeds from it, posteriorly ending in a thickened semioval plate.

The opercular appendages of only two specimens have been observed. These represent the female appendages of young examples. The best preserved and oldest specimen gives two aspects of the appendage, the exterior on the mold of the fossil, and a partially interior one on the cast. Both together show that the appendage was broadly hastate at the anterior end, extending to nearly the anterior margin of the operculum and was produced posteriorly with a clublike process which, in the young individuals at least, did not extend beyond the posterior margin of the operculum. This process was overlapped on both sides by the inner margins of the two opercular plates, which left only the narrow median portion exposed.

In the largest of the specimens, a distinct sigmoid vermiform depression is seen to proceed on one side from the anterior end of the appendage, passing just within the anterior margin of the opercular plate for some distance and finally swinging backward, gradually tapering toward its extremity. This depression corresponds in location and form to one of the paired horn-shaped organs observed by Holm in  on the inside of the operculum on either side of the opercular appendage. It could be well conceived that its presence prevented the filling of the space with mud for a time and its final collapse produced the depression. The opposite opercular plate is bent over and crumpled so that this hornlike organ is not there observable.

Sculpture. The sculpture of the carapace consists only of fine tubercles which are most distinct and closely arranged along the margins and between the eyes; that of the remainder of the integument is composed of linear, crescentlike or angular scales.

The scales of the tergites are small, mostly linear or flat crescentic and distributed on the anterior half of the tergites. The sternites are entirely covered with large, prominent scales except in a belt along the posterior