I20 NEW YORK STATE MUSEUM 
The closer approximation of the lateral eyes to the margins in the 
young than in the adult eurypterids is a feature shared to some extent 
by young Limul and still more distinctly shown by the embryo of the 
scorpion [Laurie, 1890, pl. 17, fig. 45]. In Limulus the lateral eyes 
and ocelli are placed on distinct ridges, termed by Packard [1870, p. 168] 
the ophthalmic ridges, which separate the cardio-ophthalmic region from, 
the lateral regions of the carapace. These ridges are most prominent in the 
larva and become obscured in the adult. They are faintly seen in the 
later embryonic stages and are there distinctly farther away from the 
median line of the carapace. The ocelli appear first on the under side of the 
head [Packard, p. 168] just in advance of the chelicerae and in later 
embryonic life wander to the upper side. 
Strabops of the Cambric has the lateral eyes in about the position 
where they are seen in nearly all our larval eurypterids; E.megalops 
(Frankfort) and the Clinton E. prominens as well as the primi- 
tive Hughmilleria also have submarginal eyes, and we see in this 
approximation of the eyes to the margin a palingenetic feature which prob- 
ably points to ancestors with submarginal eyes. In the Frankfort Lower 
Siluric fauna taken as a whole, the eyes are nearer the margin, a note- 
worthy fact in this connection. The genera Pterygotus, Simonia and 
Eusarcus make a nearer approach to the primitive condition in this respect 
than Stylonurus and those species of Eurypterus with approximate eyes 
high up on the carapace. A comparison in point is afforded by the trilo- 
bites, in which, according to Beecher’s excellent investigations, the eyes 
appear on the under side in both the ontogenetic and phylogenetic 
development. 3 
The prominence and great size of the ocellar mound in the larvae of 
the eurypterids are fully in consonance in function with the early appear- 
ance and relative great size of the ocelli or “larval eyes ’’ in the embryo 
and larva of Limulus and the great size of the central eye in the scorpion. 
There is no direct evidence to indicate that the prominence of the ocellar 
mound is of any other than larval or coenogenetic character. 
