mens. It does not differ materially in form from the same part in the British and Russian species. It is longer than any tergite, its length being one fourth of the width; and its posterior margin has, as pointed out by Woodward, the form of a bracket, while the anterior margin is gently concave and the lateral margins run obliquely forward and inward, the anterior angles being distinctly rounded away.
The transverse line of the operculum, which has hitherto been observed only in Eurypterus, is quite distinctly seen near the margin of the right half of the operculum and can be traced to about one half the distance to the median suture.
The four following sternites are readily distinguished from the tergites by their greater length and the round sweep of their lateral margins. The antelateral angles have not been seen in our specimens on account of the strong overlap of the sternites which must have amounted to fully one half the length of the plates. The doublure of the posterior margin is narrow. The median suture is visible in the operculum and the next sternite. In specimen plate 77, figure 3, the third sternite has split with a straight cleft, thus indicating a line of weakness where the suture might be expected. The doublure of the posterior margin is narrow, amounting to only one fifth of the exposed part of the sternite [pl. 72]; and in the operculum it seems to have been reduced to a narrow band but 1 mm wide in mature specimens. The lateral doublure is well seen on the left side of the specimen; it attains the width of the posterior doublure in its postlateral angle but narrows so rapidly that it does not reach the antelateral angle.
Postabdomen. The postabdomen of this species exhibits the features of that of P. macrophthalmus with the exception of the ultimate segment which in mature individuals [pl. 76] abruptly flares out, at one fourth its length, into rounded wings that increase the width of the segment by one fourth. The edge of these alae is coarsely serrate.[1] The median
- ↑ The form of this edge and the peculiar shape of the entire segment led Pohlman to the erection of a new species, P. quadraticaudatus, on the supposition that it represents a telson.
