Ontogeny of Stylonurus myops
Among the early stages of eurypterids obtained at Otisville is a number of very minute individuals, that are noticeable for their owllike appearance due to the very broad, anteriorly emarginate carapace and their immense hemispherical and disklike eyes [pl. 51, figs. 1–6]. Although there is a considerable gap in size in the series of these specimens and of the smallest of the carapaces [pl. 51, figs. 7–9] which undoubtedly belong to S. myops, these small entire individuals seem properly referred here, for the following reasons: The form of the carapace is clearly that of S. myops which is the only one in the Otisville fauna possessing a subrectangular outline; the position of the eyes corresponds to that found in the adult stages of S. myops; the broad rim of the carapace, a characteristic feature of S. myops and not observed in other members of this fauna, is present in these young individuals.
In surveying this whole series, one distinguishes three ontogenetic groups, the first represented by the small entire individuals on plate 51, figures 1–6; the second by the group plate 51, figures 7–14, and the last by the specimens plate 52, figures 1–4, 10. As the smallest specimens of the first group are but little larger than the eggs of Limulus and are thoroughly larval in their character, we consider them as representing the nepionic stage. The next group which is intermediate in its character between the first and last may be considered as representing the neanic growth stage, since the last group belongs to specimens of ephebic or mature age, as far as we can judge, although we suspect that these are only the earliest ephebic substage.
The nepionic stage is again subdivisible as far as our material is concerned, into two substages. The first of these, illustrated by the figures 1–3, [plate 51] is characterized by (1) the relatively large size of the carapace to the body (proportion as 1 : 3.75 in the former and as 1 : 5 in the latter); (2) the evenly terete or conical form of the body which makes the carapace also the broadest part of the integument; (3) the presence of a distinct border surrounding the whole carapace; (4) the immense size of the
