THE EURYPTERIDA OF NEW YORK 163 
[pl. 5, fig. 5], the marginal portions but slightly flatter than the rest; in many 
partly compressed specimens [pl. 4, fig. 4] the axial part remains prominent, 
as in the axis of the trilobites, while the lateral parts assume an aspect 
similar to that of the pleura. They are depressed and slightly raised toward 
the margin and bent specimens show on the inner side folds that are 
slightly curved and pass obliquely forward. The first tergite is narrower 
than the others and its postlateral angles truncated like those of the cara- 
‘pace. Its length is about seven and one half times the width. The middle 
portion of the tergites is broadly arched forward, while the lateral portions 
are normal to the axis of the body or again curve forward. The antelateral 
angles are produced into articulating lobes. The tergites overlap along 
their anterior margins about one sixth their length. The posterior doublure 
is about one fifth the length of the segment. The ventral side of the pre- 
abdomen appears to have been more convex than the dorsal, for in com- 
pressed specimens the edges of the ventral plates project on both sides 
beyond the dorsal plates [pl. 4, fig. 4]. Probably the ventral median 
line was somewhat depressed, as in E. microphthalmus. The 
_ five sternites are longer than the tergites, medially cleft, bounded by straight 
transverse anterior and posterior margins and, with the exception of the 
operculum, are furnished with large rounded antelateral lobes. The oper- 
culum is longer than the other sternites, its antelateral angles are rounded 
off, while the anterior edge is produced into a broad median lobe. A like 
lobe is observed on the second sternite in the female. The postmedian 
angles of the two opercular plates are also produced into lobes, while those 
of the following sternites are well rounded. 
The postabdomen is one third as long as the whole body. From the 
first to the sixth segment the width decreases by three fifths of the width 
of the first segment, while the length of the last is double that of the 
first. The first differs in appearance from the others in having the lateral 
margins strongly convergent backward, thus resembling the preceding 
tergites, while the others have subparallel lateral margins. Likewise the 
first segment has broadly convex anterior and equally concave posterior 
