188 
PALEONTOLOGY OF NEW YORK. 
antero-lateral edges the margin is strongly thickened, on the postero-lateral 
edge being broadly infolded, and its thickened edge continuous with the 
posterior spine. This ridge on the doublure is distinctly marked upon the 
upper surface of the carapace when compressed. 
The Cephalic region is gently convex and bears a strong, somewhat elongate 
eye-node, situated just in front of the extremity of the lateral carina, and 
toward the dorsal line. The summit of this optic node bears a deep pit or 
invagination, which may have held a lense or series of lenses, or it may be 
evidence of a more embryonic character in the visual organs. Upon the 
thoracic region is a strong, straight carina, extending its entire length. Its 
sides are broadly sloping, and well-preserved individuals show a finely incised 
longitudinal line about half way up each slope. On the inner slope, be¬ 
tween this line and the summit of the ridge, there is a series of oblique 
crenulations. 
The Surface is ornamented by a number of low tubercles in the inter-ocu¬ 
lar region, and elsewUere over the cephalic area by fine, elevated, frequently 
anastomosing lines; upon the extra-carinal area these lines become longer 
and more continuous. Otherwise the surface is minutely punctate or 
granulose. 
Abdomen composed of two somites of which the anterior was probably almost 
concealed beneath the carapace. This somite is short, one-half as long as 
wide, and slightly elevated at the margins into articulating ridges; the 
posterior somite is quadrate and somewhat longer than wide. The sur¬ 
face of both somites is ornamented by strong, elevated, venate lines, which, 
upon the anterior joint, radiate from the crenulated margins and are directed 
forward, and upon the posterior they also radiate from the margins but are 
directed inward and backward. In one specimen these lines are crossed by 
a series of fine, parallel wrinkles, which appear to be due to compression. 
The posterior somite bears a few low, broad tubercles. 
Post-abdomen. Caudal plate sub-triangular on the ventral surface, distinctly 
ridged on the anterior extremity for articulation with the last somite; sub- 
