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 ftfth 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 Pterygottu have ever existed in Eurypterut, they must have 

 been very small, and situated in advance of the first designated pair of feet, and may have resembled those 

 of Limulut. In two instances I have seen !ome indication of a small appendage in this position, but a farther 

 cxaminatiou does tiot offer any conftrmation of this view. 



