THE EURYPTERIDA OF NEW YORK 317 
posterior parts contracted. In the young specimen, the length is to the 
width as 7:8, in the ephebic example, as 8:9. It is widest in the 
middle portion and contracts again by about one seventh of its width 
toward the base. The doublure is about 3 mm wide in the type speci- 
men and relatively wider in the young. It diminishes in width poste- 
riorly and finally runs out. The margin of the carapace is bounded by a 
thickened border, behind which several parallel striae are observed. The 
eyes are somewhat indistinct in the specimens; they appear to have been 
large and consisted of almost circular visual surfaces surrounding circular 
prominences. The latter occupied one fifth of the length of the carapace, 
were situated on the anterior half and not quite twice their width asunder. 
The ocelli have not been seen. The preabdomen is relatively very short 
(its length amounting to only two thirds that of the carapace) and 
broad (proportion of length to width as 4:5), its greatest width being 
attained in the region of the fourth tergite whence it contracts rather 
rapidly. At the widest part of the preabdomen, the tergites seem to be 
about six and one half times as wide as long. Their general form is but 
indistinctly discernible in the carbonaceous film, but seems to have been 
that of straight transverse bands. The operculum is not appreciably wider 
than the other sternites and the next sternite fully as wide. The details 
of the outlines of these and the following sternites have not been made 
out. The third sternite (the widest) is, in its exposed or not overlapping 
part, eight times as wide as long. The posterior margins are uniformly 
concave, the curvature increasing in the succeeding segments. The median 
suture is well seen in a young specimen [pl. 2s, fig. 3]. The post- 
abdomen shows an immense development; it is nearly as long as the cara- 
pace and preabdomen together and occupies about one third of the total 
length of the body. The first postabdominal segment still corresponds 
in anterior width to the preabdomen, but it contracts so rapidly that its 
posterior margin is shorter by one fifth and the final width of the post- 
abdomen is but one third of that at its beginning. While thus the post- 
abdominal segments diminish greatly in width posteriorly, they increase 
