THE EURYPTERIDA OF NEW YORK 135 
oval preabdomen and narrow taillike postabdomen, anteriorly longest 
series of endognathites, curved telson and other features, this genus bears 
marks of a peculiar aberrant type that apparently left no successors. 
‘VI 
TAXONOMIC RELATIONS 
Any inquiry into the zoological position of the eurypterids must be 
based on that of Limulus since there is little doubt in the minds 
of paleontologists of the close relationship between the eurypterids and 
the king crab. In fact, all recent investigations and discoveries of euryp- 
terids have only served to bring out new homologies of structure between 
the two groups. Nieszkowski, Hall and Woodward among the earlier 
writers on eurypterids clearly recognized and distinctly pointed out the 
numerous homologies and united the eurypterids and xiphosurans. They 
were especially successful in correlating the segments and the appendages of 
the cephalothorax. Later Schmidt and Laurie established the fact that 
the Eurypterida had four pairs of platelike abdominal appendages that 
bear the branchiae on their posterior surfaces and constitute another 
important homology with Limulus. Finally Laurie and Holm indicated as 
a further common structure the existence of preoral appendages in the 
eurypterids. Holm especially demonstrated this close relationship with the 
limulids, by the description of a number of finer details of organization: 
the occurrence of epicoxae in the second to fourth endognathites, the 
presence of a circular hole spanned by a thin membrane in the coxa of 
the fourth endognathite. We believe we have added to this array of 
evidence some further important details in identity of structure of the com- 
pound eye of Pterygotus and that of Limulus, and of the general parallelism 
in the ontogeny of the eurypterids and Limulus. The former argument is 
considered of especial significance as the eye of Limulus has been shown 
by Watase and others to be of a type of structure entirely peculiar. In the 
chapter on ontogeny we have not expressly pointed out the similarities 
and differences in the individual development of the eurypterids and 
