THE EURYPTERIDA OF NEW YORK 159 
acters, especially in the clawlike development of the ninth or terminal 
segment of the swimming leg, and it is made the type of the subgenus 
Onychopterus. Eurypterus prominens has a long carapace 
with eyes well forward, characters that are also present in the young of 
E.remipes. Eurypterus boylei, from the Guelph forma- 
tion, also exhibits proof of aberrant development in the large median 
tubercles of the tergites. Group (c) shows distinct phylogerontic char- 
acters in the strong development of the spines, surface scales and other 
excrescences, as well as in the large epimeral pieces of the postabdominal 
segments, and these are comprised under the subgeneric term Anthra- 
conectes. 
The group Eurypterus sensu stricto, or as represented by division (a), 
embraces not only the relatively simplest expression of the genus around 
which the other forms quite naturally group themselves, but also the 
most vigorous and that which dominates the stage (Salina) where the genus 
clearly reaches its climacteric development. The Eurypteri of the Bertie 
waterlime, notably E.remipes and E. lacustris, are there- 
fore properly considered as representing the typical expression of the genus. 
The genus thus defined is characterized by an elongate, slender body, 
widest in the middle of the preabdomen and distinctly differentiated into 
preabdominal and postabdominal regions. The carapace is subquadrate 
to subrectangular in outline, with rounded anterior angles, relatively 
small, one fifth to one seventh the total length of the body. The com- 
pound eyes are reniform, without distinct facets; situated on the dorsal 
side of carapace. The ocelli are situated between the compound eyes. 
The chelicerae are small, not extended beyond the edge of the carapace. 
The endognathites increase in length from the first backward; the first 
three pairs relatively robust, short and spinous; the fourth pair slender 
and bearing only a terminal spine with two spines on the penultimate 
segment. The fifth pair is developed into swimming legs with bladelike and 
extended seventh and eighth segments. Its ninth segment is rudimentary. 
The ventral membrane of the cephalothorax is separated by a distinct suture 
