| The largest carapace observed measured | millimeters | |
| Length of carapace | 19. | |
| Width | 27. | |
| Length of lateral eye | 6.9 | |
| Distance between visual surfaces | 12.8 | |
Horizon and locality. One of the rarer forms in the Shawangunk grit at Otisville, N. Y.
Remarks. The principal features which characterize this species as belonging to Stylonurus are the broad, furrowed doublure, the large size of the eyes, the semicircular outline of the visual surfaces and their approximate position and the rows of tubercles along the posterior margins of the tergites. In the general outline of the carapace and its relative dimensions S. myops may be compared to S. powriei, megalops and scoticus. The great size of its eyes recalls S. megalops and, as in that little known Scottish form, the visual surface extends over more than a semicircle. Its prominent ornamentation distinguishes it from all of these species.
The later collections from Otisville have afforded some carapaces [pl. 51, figs. 8–12] of very young individuals (width but 5 mm) which differ so much from that of the mature type that they would be easily taken as representing a different species. They are broader and shorter and semicircular to semielliptic in outline. The lateral eyes are close to the margin instead of approximate; and their visual surface is relatively less extensive. The entire surface is so densely covered with tubercles that it has a shagreen aspect. Most of these ontogenetic characters are probably of phylogenetic importance, especially the change in the form of the carapace and in the position of the eyes. These have been noted more fully in another place.
A number of specimens [pl. 51, fig. 14; pl. 52, fig. 9] exhibit a distinct acute process in the middle of the frontal doublure. The same specimens are also relatively a little shorter. For this reason we consider it possible that both these features are due to a slight lateral compression,
