154 
PALEONTOLOGY OF NEW YORK. 
The description of the fossil is as follows; 
Outline 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 surfiice, 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 LimuUdcR 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 
of 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 and 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 
