THE EURYPTERIDA 
I 
MORPHOLOGY, ANATOMY AND TERMINOLOGY 
General form. The body of the eurypterids, as a rule, is elongated, 
and often somewhat fishlike in dorsal view, but it may also become dis- 
tinctly scorpioid. The slender fishlike form is typically expressed by 
Hughmiulleria [see restoration, pl. 59] where the body expands but slightly 
‘in the anterior third and then tapers very gradually to the caudal spine; 
the head shield is semiovoid and the body less depressed than in other 
genera. Pterygotus is similarly built, but the head shield is more rounded 
in front and some species are broad and plump. In Eurypterus the lateral 
expansion or flattening of the body becomes manifest in both head shield 
and abdomen and the contraction of the body to the caudal portion is more 
abrupt. Stylonurus has a slender body which, however, expands gradually 
beyond the middle and then contracts more rapidly. In Slimonia a 
scorpioid appearance is produced by the squarish head shield and the © 
long tubular caudal portion of the abdomen. An extreme differentiation 
from the slender terete body of Hughmilleria is reached in Eusarcus with 
its triangular head shield, broad flat body with subcircular outline, from 
which the long narrow tail is sharply set off. 
We shall recur to this variant expression of the body and its bearing 
on the mode of life of these animals after a consideration of the 
appendages which are correlated to the form of the body and corroborate 
the evidence from the latter. 
Integument. The body is covered by a chitinous exoskeleton which 
alone is preserved in the rocks and usually compressed into an extremely 
tenuous, carbonaceous, more or less wrinkled film. (Notwithstanding 
its thinness it must have been, like the tough leathery integument of 
Limulus, very strong and able to furnish a stout basis for the powerful 
muscles of the creatures. 
23 
