THE EURYPTERIDA OF NEW YORK 235 
and this median convexity grades into the round postabdomen. The ven- 
tral side of the preabdomen was more strongly and uniformly convex than 
the dorsal. In outline the abdomen widens so rapidly that at the third and 
fourth dorsal segments, where it is broadest, it is already more than twice 
as wide as the head shield at its base. With the next two segments it con- 
tracts abruptly to the postabdomen. 
Preabdomen. ‘The tergites are broad, short plates; those in the middle 
are five times as broad as long. First tergite much shorter than the 
others, its posterior margin parallel to the posterior margin of the carapace; 
anterior margin uniformly and deeply concave, the segment having a shape 
approaching a crescent; antelateral angles produced into blunt ears. In 
-most specimens this plate is pushed under the cephalothorax, sometimes, as 
in the type, so much that only its posterior margin remains visible. Second 
tergite also very concave in front, its antelateral angles projected forward. 
Posterior margin with a low broad concavity in the middle. This and the 
following tergites are much longer in the lateral than in the middle portions. 
The five sternites or ventral segments are strongly curved forward and 
convex, of relatively great length, the latter amounting to one fourth of 
the width in the typical middle plates of the series. 
Operculum differing from the following plates in outline but little 
if any longer. Anterior margin not seen in perfect preservation, but 
the evidence at hand indicates that the antelateral angles were truncated 
and well rounded and the remainder of the margin straight transverse. 
Posterior margin notably less curved backward near the sides than the 
following sternites, but produced into two prominent blunt lobes at either 
side of the median cleft. 
The other sternites possess a double curvature. They are strongly 
curved forward in the middle half. The anterior margin becomes so 
deeply concave on either side that a middle transverse line passing 
through the center of the last sternite will touch the interior edge of 
these sinuses. _The antelateral angles are produced into prominent ears. 
Corresponding to the anterior margin the posterior margin shows two 
