352 NEW YORK STATE MUSEUM 
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 ante- 
lateral 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 frag- 
mentary condition. 
Postabdomen. The five first postabdominal segments are, on the 
whole, simple broad rings, indicating that the original form of the post- 
abdomen 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 doub- 
lure of the posterior margin is narrow. 
The sixth postabdominal segment differs materially from those pre- 
ceding 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 spect- 
mens, 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 strength- 
ened by a thick ridge along the middle line which runs out into a blunt 
