THE EURYPTERIDA OF NEW YORK 125 
shorter than wide. In all eurypterids the preabdominal segments are 
greatly wider than long and it is hence safe to infer that the carapace also 
was originally wider than long, and to assume for the prototype a small, 
short carapace of the width of the preabdomen. 
In one section of the eurypterids the lateral eyes are marginal and 
faceted, and in the other situated on the dorsal surface and smooth. It 
is important to determine which of the two forms of eyes is the more 
primitive. Laurie has argued in favor of the eyes of Pterygotus, representing 
the first group, basing his view on a comparison with the trilobites (on the 
assumption that the eurypterids are derived from the trilobites), the 
Scorpionidae and Thelyphonidae, ‘‘ which must be derived from some way 
down the eurypterid stem.’’ The Lower Siluric fauna is constituted of 
species with submarginal eyes and this fact seems to favor Laurie’s view. 
It is a proper assumption that the appendages of the prototype were 
undifferentiated. Those of Strabops are unknown with the exception of 
two segments of the last pair which indicate a primitive form of append- 
age, and eurypterid larvae have also failed to afford any conclusive 
evidence bearing on this point. The Siluric genera all exhibit far-reaching 
differentiation in the legs; this manifests itself especially in the last pair 
which has been variously transformed either into broad and strong paddles 
or excessively lengthened; the preoral appendages have been developed into 
enormous pincers in at least one genus, Pterygotus, but the four pairs 
of walking legs which lie between these extremes have remained relatively 
simple in construction, especially so in Pterygotus where all four are alike, 
rather slender and without spines. Laurie has regarded the simple char- 
acter of the Pterygotus legs as an argument in favor of the primitive 
character of the genus. While we do not share this view we agree as to the 
manifest primitiveness of these four pairs of legs and therefore assign such 
appendages to the prototype.' In Eurypterus the fourth pair has also 
‘Laurie has also advanced as a point in favor of the primitive condition of 
Pterygotus “the apparently much greater development of the epicoxite—a structure 
common to the eurypterids, Limulus and Scorpion, and therefore probably primitive—in 
Pterygotus than in. the other genera’’ [op cit p. 521]. The evidence in regard to 
Eurypterus since obtained by Holm shows that the epicoxite is as strongly developed 
as in Pterygotus. | 
