30 | NEW YORK STATE MUSEUM 
fischeri. Such minute pores or canals may have given passage to 
sense organs (sensory setae or bristles) or to tegumentary glands. 
Serrations and spines. -The edges of the integumental plates are 
frequently furnished with sharp serrations, like those of the abdomen of 
Limulus. These serrations are especially frequent on the anterior edge 
of the palette of the swimming leg, on the epimera of the postabdominal 
segments and on the lateral edges of the tail spine. In Eurypterus the 
distal edges of the segments of the swimming legs are also dis- 
tinctly serrate. Frequently an alternating series of larger and smaller 
serrae is found. A goodexample of this is the telson of Pterygotus 
buffaloensis. | 
The spines on the legs and those on the manducatory edges of the 
coxal segments have originated from fine hairs, which grew first into strong 
bristles and finally into spines. These spines become powerful spurs in 
some genera, as Eusarcus and Stylonurus. In Ctenopterus, the subgenus 
of Stylonurus, they are sometimes broadened and may have assisted in swim- 
ming. Like the hairs, the spines are inserted and fixed by ringlike swellings 
of the integument at their bases and frequently broken out, leaving dis- 
— tinct scars. 
Cephalothorax. The body of the Eurypterida consists of 18 segments 
and is functionally divided into two sharply distinct regions, the cephalo- 
thorax or prosoma, consisting of six fused segments and the abdomen con- 
sisting of 12 segments. The cephalothorax with its appendages is specialized 
for locomotion and prehension, while the abdomen 1s essentially a vegetative 
sac. The six segments of the cephalothorax find their expression in the 
six pairs of appendages. The cephalothorax consists of the carapace or 
head shield and the organs of the underside. 
The carapace is of small size, one fifth of the body (exclusive of the 
telson) or less in length. This small size is a feature that gives the euryp- 
terids a greatly different aspect from Limulus with its immense semi- 
circular carapace, but it well corresponds to the relative dimensions in the 
scorpions. In Limulus it is expanded so much both laterally and frontally | 
