the neanic stage the body had overtaken the carapace in growth. We judge that in this individual the carapace was not longer than one fifth the entire body. The carapace of the nepionic stage is also wider than any other part of the body, the latter tapering directly from the base of the carapace to the tail.
The imperfection of the body is very apparent in the first individual, which probably had no more than six or seven segments and the next but eight or nine without the telson. The segments are all of equal length, but diminish rapidly in width, while in the mature Pterygotus they gradually widen to the fourth and thence again very gradually contract to the telson.
The compound eyes are, in contrast to the nepionic stages of the other eurypterids, not relatively larger than in the ephebic stage, but rather smaller. This peculiar difference is quite apparently due to the fact that the mature Pterygotus has relatively larger compound eyes than the other genera and we may infer from this relation of the nepionic to the ephebic eyes, that the large eyes of Pterygotus are a further development of a feature larval in the whole class. While the nepionic eyes were not relatively larger than those of the mature individuals they seem to have been somewhat more prominent or bulging. The first of the nepionic specimens [pl. 81, fig. 1] exhibits two very distinct tubercles near the anterior margin which, if ocelli, would have a position corresponding to that in the embryo of Limulus polyphemus.
The telson of the nepionic stage has unfortunately not been seen. We surmise that it would give interesting clues as to the development of the bilobed telson characteristic of Erettopterus.
The specimen figure 2 exhibits a distinct cleft or rupture, slightly more irregular and curved than figured, extending over the posterior part of the carapace and the following segments. This may be the result of molting. Considering the small size (1.5 mm) of the specimen, it is quite possible that this was the first molt after hatching.
The neanic stage is represented by the two specimens figures 3, 4.
