396 
PALAEONTOLOGY OF NEW-YORK. 
extends to the third or fourth : this appendage is jointed towards its 
extremity, and terminated by two slender, flexible ? processes, and has 
apparently been'capable of considerable freedom of motion. The remaining 
joints of the lower side of the body present no conspicuous differences 
from those of the upper side. 
The mouth is placed centrally beneath the carapace, and surrounded 
by four pairs of small jointed feet, and a fifth larger pair. The three 
anterior pairs are similar to each other; and several of the joints are 
furnished at their distal extremities, on one or both sides, with a small 
articulating spine, and the terminal joint consists of a long spine. The 
fourth pair of feet are more slender, and the joints longer. The fifth pair 
of feet are natatory, longer and more dilated than the others, and placed 
beneath the posterior margin of the carapace. The basal joints of these, 
consisting of broad rhomboidal plates, are serrated on their inner anterior 
approximate margins, and thus fitted for performing the functions of jaws : 
together they cover nearly the entire width of the lower part of the 
carapace, and extend a little below the line of its posterior margin. Lying 
over the inner edges of these plates is a longitudinally oval, ovate, or 
cordiform central post-oral plate, at the anterior sinuate margin of which 
is very clearly the entrance into the mouth : towards this, the bases of 
the five pairs of organs are all converged*. 
The surface of the head and parts of the body is often finely granulose ; 
and that of the articulations, the bases of the joints, and sometimes other 
portions, are marked by an imbricating scale-like sculpture. These scale¬ 
like facets are of varying size and elevation, and rarely closely arranged. 
There are sometimes four or six rows of more prominent pustulose scales 
arranged along the centre of the back to the base of the thoracic arti¬ 
culations, while two similar rows mark the last six joints. 
The texture appears to have been elastic or leathery, and the substance 
very thin. 
* If chelate appendages similar to those of Pterygotus have ever existed in Eurypterus, they must have 
been very small, and situated in advance of the first designated pair of feet, and may have resembled those 
of Limulus. In two instances I have seen some indication of a small appendage in this position, but a farther 
examination does not offer any confirmation of this view. 
