THE EURYPTERIDA OF NEW YORK 305 
eyes, which occupy the entire space between the border and a median 
ridge; (5) this distinct median ridge, also a character not observed in later 
stages, and finally the abdominal segments which are (6) less in number 
and (7) lack all differentiation between preabdomen and postabdomen 
as far as the length of the segments is concerned, all being of equal 
length. 
We may now consider some of these larval characters in somewhat 
greater detail. 
The carapace appears to have had more distinctly the nature of 
a definite shield than at any later stage, for it is here most clearly set off 
by a flat thickened border of equal width. The same impression is also 
conveyed by the rounded postlateral angles, well seen in figures 1 and 3.' 
The large size of the carapace, its distinction from the abdomen and the 
broad border, are features which this larva has in common with Limulus 
[text fig. 24], with the difference, however, that in the latter the border is not 
continuous over the posterior margin. But there are still other features 
inviting comparison with the larva of Limulus, notably the median ridge, 
which produces a trilobation of the carapace directly corresponding to 
that of Limulus in the so called “trilobite stage.’ It further appears 
that the number of segments of the abdomen may be the same as that 
observed in the larva of Limulus shortly after hatching, that. is nine in- 
cluding the rudiment of the caudal spine. Eight (including the telson) 
are distinctly visible in the original of plate 51, figure 4, but it is probable 
that the first segment is hidden under the carapace. As in the larva of 
Limulus these segments are not differentiated, at least in their dorsal 
view and the telson spine is still extremely rudimentary. But herewith 
all similarities end. 
The uniformly terete form of the abdomen of this larva is in strong 
contrast to the broad, posteriorly widening abdomen of the Limulus 
larva. There is little doubt that the latter represents a tachygenetic 
‘In specimen figure 2 the apparent posterior margin of the carapace is probably 
formed by the first segment underlying 1t. 
