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 approximate [as in pl. 52 fig. 1–4] and thereby assume the position characteristic to most species of Stylonurus.

The neanic and ephebic stages exhibit a strong tubercular ornamentation of the carapace and segments. No indications of this have been observed in the nepionic stage, a fact that may be attributed either to a failure to observe it on account of the extreme smallness of the specimens or to its absence. We believe the latter to be the case for several reasons. One of these is that the largest specimens of the nepionic stage [figs. 5, 6] could have hardly failed to show traces of this sculpture if it existed, and another, that the smallest carapace of the neanic stage observed [fig. 8] possesses this tubercular sculpture only in an incomplete or but partially developed form. Moreover, the fact of the absence of the ornamentation of the mature forms in the larvae is fully in accordance with the relations of the larvae and mature forms in most other arthropods.

The neanic stage, typically represented by figures 7–13, is distinguished from the ephebic stage mainly by two characters, the relatively greater width of the carapace and the submarginal position of the compound eyes. In the carapaces, plate 51, figures 9, 11, 12, the average relation of length to width is as 10 : 16 and in plate 52, figures 1–3, as 10 : 14.

Actually the relative length of the carapace increases but little (about one eighth) with advancing age but the fact that in the neanic stage the anterior angles of the carapace are strongly truncated and rounded and in the mature stage subrectangular, assists greatly in increasing the appearance of smaller length and greater width in the neanic specimens. Specimen figure 14 which has almost the size of the mature specimens, still