250 NEW YORK STATE MUSEUM 
In this nepionic individual the relative width of carapace is much 
greater than in the type. The impression of excessive width is, however, 
hightened by the lengthening of the genal angles parallel to the base of the 
head. These horizontal genal spines, together with the equally produced 
third frontal angle of the triangle, serve: to strongly emphasize the 
triangular aspect of the head. The frontal projection is the forward 
continuation of a strong median crest extending forward from the base. 
The lateral margins exhibit the sigmoidal curvature and the cheeklike 
convexity of the posterior portion as in the following stage. 
The compound eyes are oval in form, of great size (about one third 
the total length of the head), strongly divergent and placed in the middle 
of the head instead of forward and farther inward from the margin than in 
the older individuals. The fact that they are surrounded by a deep depres- 
sion seems to indicate that they were originally quite prominent, thereby 
drawing the surrounding test downward with them in becoming depressed 
to the level of the carapace. The ocelli have not been discerned. Finally . 
the carapace exhibits a broad thick margin on all three sides, possibly a 
broad doublure on the under side. | | 
It is easily seen that this larval form, notwithstanding its own peculiar 
characters, shares its most important features with the larval stages of 
other eurypterids. This is especially true of the large size of the eyes, 
the great width of the head and the presence of a median crest. The acute 
lobes of the angles are a character peculiar to this larval form and perhaps 
in line with the spinose processes of the larval forms of many crustaceans. 
The position of the compound eyes in the middle of the head may be of 
phylogenetic significance and indicate the secondary acquirement of the 
frontal position of these eyes in Eusarcus. It should be also noted that 
the convergence of the eyes in the mature form is directly reverse to that 
in the larval stage, obviously a consequence of the later adjustment in 
position of the compound eye to the converging frontal margins. 
Measurements. The length of the type (carapace) is 3.2 mm; its 
width 4.8 mm; the width of the carapace of the original of plate 36, figure 5 
