l-,l PALEONTOLOGY OF NEW YORK. 



The description of the fossil is as follows: 



( (inline of the BODY (cephalothorax and abdomen) sub-circular or slightly ovate, 

 the genal spines scarcely protruding to interrupt the regularity of the 

 outline. 



Cephalothorax sub-semicircular in outline, genal spines produced as far as the 

 tip of the first abdominal spines. The infolded frontal border is broad and 

 convex anteriorly, narrowing to the base of the genal spines. In the axial 

 line its edge, or a ridge upon its surface, appears to be connected with a bi- 

 symmetrical, trifoliate plate, which lies in front of the probable position of 

 the mouth and extends backward, its largest lobe lying in the axis. This 

 has been regarded by Mr. Williams as possibly an hypostomal plate. It may 

 be suggested, that if this body were continuous with the frontal border the 

 apparent posterior margin of the doublure might be regarded as a sharp 

 ridge upon the lower side, curved backward in the axial line, similar to that 

 in Limulus and Prestwichia. Such an interpretation of this character is not 

 unsupported by the appearance of the fossil and obviates the necessity of 

 supposing the animal to have differed from the Limulida in the possession of 

 an hypostomal plate, while agreeing in other respects. Behind the margin 

 of the infolded test, lies a series of indistinct impressions of narrow append- 

 ages, of which three and possibly four pairs are discernible. They appear to 

 be centered about a cavity close behind the apex of the doublure and to bend 

 outward and upward in a broad curve. Near the genal spines on either side 

 is a conspicuous, irregularly striated area, which Mr. Williams has suggested 

 may be the impressions made by the foliaceous terminations of the last pair 

 nl limbs; they are certainly very suggestive of such an origin. 



Behind these appendages and situated at about the center of the surface 

 of the fossil is a transversely-elongate, triangular impression having the 

 position of the thoracic or opercular plate in Limulus 'Ami the Eurypterida. The 

 apex of this impression lies in the axial line, its lateral slopes are long and 

 its Length is less than one-half its width along the posterior margin. Two 

 parallel longitudinal furrows divide it into median and lateral areas, and these 



