302 NEW YORK STATE MUSEUM 
The largest carapace observed measured millimeters 
Length of carapace... 2.0... cee eee ee en eee IQ 
Width. 0... ee cent een eee 27 
Length of lateral eye................0.. eee eee eee 6.9 
Distance between visual surfaces........... 00.0000 eae 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 approx- 
imate 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 repre- 
senting 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 phylogen- 
etic 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 speci- 
mens are also relatively a little shorter. For this reason we consider it 
. possible that both these features are due to a slight lateral compression, 
