selected. These specimens differ from the mature stage in the following characters:
- The carapace is still relatively wider though not as wide as in the preceding stage and already approaches a semicircular shape.
- The compound eyes are still relatively large, holding a median position in proportions between the nepionic and ephebic stages. In plate 21, figure 9 the length of the eyes to the length of the carapace is as 3 : 7, while in the nepionic stage they are as 3 : 6 and those of the ephebic stage as 3 : 9. They are also distinctly nearer to the frontal margin than in the mature specimens and the ocular nodes are more prominent than in later stages. They still show a distinct tendency to converge forward. The crescent visual surface is now distinctly seen, but it appears still broader than in the mature stage.
In many examples of this stage the ocellar mound is so large and distinct that its greater size and prominence in more youthful stages may be legitimately inferred [figs. 3, 4, 8, 10].
The abdomen in these neanic specimens is already as slender as in the adults [fig. 8]. One exception is the fine specimen [pl. 22, fig. 7], which is a little broader than the others. The presence of the lobes of the postlateral angles, however, indicates that this individual was flattened out before burial.
Measurements. Length of smallest nepionic individual, 5.25 mm; its width, 2 mm; width and length of carapace, 2 mm and 1.1 mm; length of compound eye, .45 mm; length of swimming foot, 1.6 mm.
An average specimen [pl. 21, fig. 12] measures in length (with the telson gone) 63 mm; its greatest width, 16 mm; the length of its carapace is 12 mm; that of the first segment 1.5 mm and that of the third 3.5 mm. The last segment is 6.5 mm long and 6 mm wide.
The largest carapace observed measures but 16 × 11 mm, so that this form is one of the small species of the genus.
Position and localities. Abundant in the fossiliferous shale of the Shawangunk grit at Otisville, N. Y.
