THE EURYPTERIDA OF NEW YORK 307 
approximate [as in pl. 52 fig. 1-4] and thereby assume the position charac- 
teristic 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 neantc stage, typically represented by figures 7-13, is distin- 
guished from the ephebic stage mainly by two characters, the relatively 
greater width of the carapace and the submarginal position of the com- 
pound eyes. In the carapaces, plate 51, figures 9, 11, 12,1 the average 
relation of length to width is as 10:16? and in plate 52, figures 1-3, as 
Io :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 appear- 
ance of smaller length and greater width in the neanic specimens. Speci- 
men figure 14 which has almost the size of the mature specimens, still re- 
‘The carapaces plate s1, figures 10, 13, 14 are obviously affected by lateral com- 
pression that shortened the width. 
* Actual measurements are as 13: 21.5 Or 10:16.5; 18:28 or 10: 15.5; and 
16.5 :26 or 10:15.8. 
® Actual measurements as 15.5 :23 Of 10:14.7; 19:27.5 Or 10:14.4; and 
20.5 : 28 or 10: 13.6. 
