Page:The Eurypterida of New York Volume 1.pdf/194

 former specimen the eyes are not only circular, at least that on the left side which is fully exposed, but this left eye is also distinctly surrounded by a thickened border, and as this border in the adult only surrounds the visual surface, the inference is suggested by this specimen that the whole node was covered by the visual area. The second specimen suggests that here the visual surface still occupied the greater portion of the node, leaving only a narrow crescent on the inner side of the node unoccupied.

The shortness of the segments, compared with their width, is a striking feature of these nepionic individuals. The preabdominal segments are from 6–9 times as wide as long, while in the ephebic stage they are but 4 times as wide as long with the exception of the first tergite which retains the nepionic dimensions. The first tergite in the first nepionic stage, shows no difference in length from the others, while in the next stage [ pl. 21, fig. 8], it is well distinguished. A specimen [ pl. 21, fig. 1] with a length of 5.25 mm has but 8 segments. One [ pl. 21, fig. 2] which measures 8 mm has already the full complement of 12. In the latter the shortness of the segments is still more striking than in the former and it appears that the insertion of the new segments took place rapidly in successive molts at the expense of their longitudinal growth. It is impossible in these young specimens to discern the boundary between the pre- and postabdomen.

The swimming legs are relatively longer and wider in the larval forms, as a comparison of figures, plate 21, figures 1 and 2; plate 21, figure 5, with plate 21, figure 11 will readily show. In the ephebic specimen the swimming leg when reflexed hardly reached beyond the third segment; in the first nepionic specimen it extends to the posterior margin of the fourth; in the second even to that of the fifth. The specimen, figure 5, also furnishes evidence of the greater size of this leg in the neanic or following stage.

The telson in the nepionic stage does not materially differ in shape and relative size from the mature condition.

Neanic growth stage. This stage is represented by a considerable number of specimens from which the originals of figures 3–11 have been