This we have identified with the nepionic stage since it can not be much older than embryonic. It is represented by the two specimens plate 21, figures 1, 2.
Herein the most striking differences from the ephebic stage are:
- The great width and small length of the body and the resulting rapid contraction from the preabdomen to the postabdomen.
- The excessive width and small length of the subtriangular carapace.
- The great size of the compound eyes.
- The shortness and great width of the segments.
- The relatively greater size of the swimming legs.
In these nepionic specimens the width of the body is to its length as 3:8, and in the ephebic stage as 3:15, hence the former stage is about twice as stout as the latter and conversely the contraction of the body is twice as rapid in the nepionic stage.
The carapace of the mature Eurypterus maria is one third wider than long (3 : 2), while that of the youngest nepionic specimen is twice as wide as long (4 : 2) and in the other much larger nepionic specimen the proportion is still 3½ : 2. The antelateral angles are so strongly truncated that the carapace approaches a triangular outline.
In this nepionic stage the compound eyes may reach one half the length of the carapace [pl. 21, fig. 3], while in the ephebic form they occupy only one third that length. They also lie farther forward and converge strongly on their longitudinal axes, while in mature individuals they either converge slightly or are subparallel. This strong convergence in the nepionic stage is continued into the neanic stage [pl. 21, fig. 9] and is in harmony with the convergence of the lateral margins. It is further to be noted that the outline of the ocular node is broadly elliptical in this stage and that the crescentic visual surface is not to be distinguished from the ocular node. It is therefore possible that the visual surface extended over the whole node and not until later became restricted to the crescent band or anterior side of this node. The appearance of these nodes as represented in figures 9 and 3 would seem to support this view. In the
