THE EURYPTERIDA OF NEW YORK _ 363 
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 visiblé 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 thatof 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 thé width of the segment 
by one fourth. The edge of these alae is coarsely serrate... 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. 
