50° NEW YORK STATE MUSEUM 
legs, giving the specimen very much the aspect of a spider crab. The 
first two of these were, however, furnished with a great number of paired 
spines or leaflike appendages of the underside. It is therefore concluded 
that in this group, for which the term Ctenopterus is here proposed, a dis- 
tinct differentiation of the legs has taken place into three spiniferous 
anterior and two nonspiniferous posterior pairs. Laurie’s Stylonurus 
elegans is a form in which a like series of at least four pairs of long 
legs is shown, the two foremost of which bear many long spines [see text 
fig. 62]. In Stylonurus proper, as represented by S. logani, the first 
three pairs of legs appear to have retained more of their original character, 
in being relatively shorter and bearing only one pair of spines on each 
segment. Still another type of differentiation, not represented in our rocks, 
is shown in 5S. scoticus Woodward. 
Eusarcus [pl. 27] represents a distinctly aberrant line of leg develop- 
ment corresponding to the entirely peculiar structure of the animal. The 
first pair of legs is of the length and character of that of Eurypterus; 
the second to fourth, however, form a series that decreases in size back- 
ward, the second being the longest of the walking legs. Correlated with 
this marked difference from Eurypterus is the greater length of the anterior 
spines on each leg. It is manifest that this creature in walking carried 
the pointed frontal part of its head shield, on which also the lateral eyes 
are found, raised high above the ground. 
In Pterygotus the four pairs of walking legs are simpler than in any 
other genus. They are of equal length, thin and nonspiniferous and were 
clearly for walking only, the prehensile function having been entirely 
transferred to the chelicerae. 
It is manifest that in the genera in which the chelicerae are very small, 
especially in Eurypterus, the walking legs with their long curved spines 
were, as in Limulus, also actively engaged in grasping prey and trans- 
ferring it to the chelicerae which transmitted it for mastication to the basal 
1We have described more fully in the generic discussion the peculiar character 
of the genus as expressed in its appendages. 
