244 NEW YORK STATE MUSEUM © 
in length the remainder of the body. The curved position of the post- 
abdomen in several specimens demonstrates the great flexibility of this 
part, while the downward curvature of the telson would make it a dan- 
gerous weapon when the postabdomen is thrown forward over the body, 
as this action. would bring the terminal spine into the position of an up- 
turned sharp pointed scimitar. 
There is a striking morphological similarity between the telson of. 
Eusarcus and the tail of the scorpion and in view of this and the acknowl- 
edged close relationship of the merostomes with the scorpions, it becomes 
a fair question whether the tail spine may not have been equipped with 
poison glands. The preservation of the telson is not such as to permit 
the determination of the presence or absence of apical pores for the emis- 
sion of the venom, or of the poison canal in the compressed spine. The 
form of the body of the animal does not suggest great agility, either in 
walking or swimming, but rather a habit of burrowing in mud or lying in 
wait for prey. In the absence of powerful prehensile organs of long reach, 
a quick dispatch of the prey must have been a necessity and this could 
have been well accomplished by an agile and venomous telson. 
The table of measurements shows that the young individual exhibits 
interesting and probably phylogenetically significant differences from the 
adult in the general proportions of its body. The most notable of these 
is the relatively greater width of the preabdomen; for while in the young 
the proportion of length to width here is as 2: 3, in the older specimens 
it is as 4:5. The postabdomen also is relatively wider or stouter than 
in the older individuals, while on the other hand, the relative lengths of 
preabdomen, postabdomen and telson to the total length have remained 
nearly the same. Still younger individuals would surely show other 
differences in these ratios. The cephalothorax which in our young and 
old individuals occupies about one sixth of the length and isa relatively 
insignificant part of the body, compared with the other eurypterids, has 
most probably lost in relative proportion during ontogenetic develop- 
ment. | 
