THE EURYPTERIDA OF NEW YORK 347 
There are nine distinct segmental division lines in the nepionic spec- 
imen, indicating the presence of nine segments, with possibly a shorter 
tenth one directly behind the head. There is a slight break in the outline 
at the end of the third segment, the fourth setting in a little further. This 
feature suggests that the postabdomen was already complete and con- 
sisted of six segments, while the preabdomen possessed thus far only three 
to four segments. This inference is supported to some extent by the fact 
that the postabdominal segments already exhibit the proportions of the 
mature forms in their gradual’ narrowing and lengthening. It is there- 
fore probable that the new segments, at least the tergites, are added in. 
successive moltings in the preabdomen, perhaps directly behind the cara- 
pace, as in the trilobites; or in other words, that the head and tail appear 
first and the thorax is completed gradually. 
The swimming legs are also shown in the nepionic specimen. They 
are relatively shorter and broader than in the mature age. 
The telson spine is of the same form and proportion to the body as 
in the ephebic stage. | ° 
The neanic stage is represented by the originals of the figures 
I-11, 13. The first two of these are fair representatives of the 
earliest neanic (ananeanic) stage. They still retain: the nepionic pro- 
portions of the carapace while the eyes have already been reduced to 
about one third of the length of the carapace, but are still distinguished 
from the ephebic eyes by their greater prominence. The large size of the 
ocellar mound and the distinctiveness of the ocelli themselves are 
also a characteristic feature of this. stage [figures 1-3]. The carapace 
is surrounded by a thick, flat border in these specimens, possibly 
the doublure of the underside, exposed by the breaking away of the upper 
margin. The preabdomen is complete in one of the two specimens 
and remarkable for its uniform width which is equal to that of the base of 
the head. As specimen figure 13 shows, this width still remains nearly 
uniform in individuals a little older, while a somewhat abrupt reduction 
takes place to the postabdomen at the first. postabdominal segment. 
