We add here several more photographs of parts of very young individuals, among them a carapace [pl. 5, fig. 1] that is much smaller than any others before mentioned (2.5 mm long). This is especially remarkable for the great size and prominence of the compound eyes, as well as of the ocellar mound, a feature that was uniformly observed in the nepionic eurypterids from Otisville. The eyes are here 1 mm long, or four tenths the length of the carapace as against one fourth or 2.5 in the mature individual. This relatively great size of the eyes in youth is still apparent in larger individuals, as that figured in plate 4, figure 4. While these eyes of the young are relatively larger than those of the adult, they still remain entirely in the anterior half of the carapace, thereby producing an appearance of more anterior position which, however, in the figure cited from Zittel-Eastman is somewhat exaggerated.
The outline of the carapace in the youngest specimen is still rounded at the antelateral corner, but soon becomes squarish as in the older ones [pl. 5, fig. 1, 2]. The carapace itself is distinctly larger in comparison to the whole body than in the ephebic stage, although on account of the distortion of one or another part of the body in every observed individual it is difficult to demonstrate this fact by measurements. In specimen plate 4, figure 1, the smallest whole individual observed, the carapace occupies fully one fourth of the whole body, while in the larger specimens it is less than one fifth the length of the body.
The swimming leg when reflexed will reach to the tenth segment or farther in young individuals [pl. 4, fig. 1–3], while in the ephebic stage it reaches only to the seventh segment. The posterior endognathites appear also to be slightly longer.
It is questionable whether the preabdomen is relatively shorter in the young at our disposal than in the adult although the Otisville material indicates that in the nepionic stage the preabdomen may well have been shorter and more abruptly contracted toward the postabdomen. In the specimens before us, however [pl. 4, fig. 1–3], the relatively greater size of the carapace produces the impression of a relatively smaller and shorter
