The middle portion forms a broad lobe while the pleurae or epimera are projected forward somewhat more abruptly. The fifth tergite is the widest, while the fourth and sixth tergites are about equally long; the fifth surpassing the other two but very little.
Along the posterior margin extends a broad doublure, amounting to one third the length of the tergite, bending forward at the postlateral angles, thence rapidly narrowing and ending a little behind the antelateral angle. Each anterior tergite overlapped the following one to an amount equal to the width of the doublure.
Such well developed "ears" at the antelateral angles as are figured by Woodward (P. anglicus) and Schmidt (P. osiliensis) have not been observed by us, but our evidence on this point is rather scanty and the following sternites of this species have been seen only in fragmentary condition.
Postabdomen. The five first postabdominal segments are, on the whole, simple broad rings, indicating that the original form of the postabdomen approached a conical shape with circular sections. There existed, however, a slight flattening along the lateral lines, in continuation of the pleurae or epimera of the tergites. The edge of these alae, at least in the fourth and fifth segments, is thickened and provided with a somewhat coarser sculpture. The anterior and posterior margins are practically straight with a slight protrusion of the antelateral corners. The doublure of the posterior margin is narrow.
The sixth postabdominal segment differs materially from those preceding both in shape and size. It is longer by one third to one half than the penultimate segment, possesses more convex lateral margins, which are serrate on their posterior half, and indications of a dorsal median crest extending over the posterior half.
The telson is obovate, one sixth longer than wide in mature specimens, and one fourth longer in young ones. It surpasses the ultimate segment in length by nearly one half but equals it in width. It is strengthened by a thick ridge along the middle line which runs out into a blunt
