CRUSTACEA. 
159 
orbital ridge. These ridges slope gradually outward, but more abrujDtly on 
their inner faces, their anterior extremities approximating the median ridge 
at its widest and most elevated portion. This median ridge is rounded and 
comparatively smooth as far backward as the posterior margin of the eyes, 
at which point it is interrupted, thence widening posteriorly into a broad, 
blunt, coarsely tubercled termination; toward the anterior extremity it 
becomes merged in the general convexity of the shield. 
The Surface of the cephalon over the anterior region has a general and 
regular convexity toward the frontal margin, becoming a little more convex 
about the anterior extension of the orbital ridges. From near the posterior 
extremities of these orbital ridges runs an irregularly sigmoid depression, 
which widens and becomes obsolete just within the baso-lateral margins. 
The median area behind the eyes is depressed-convex or flattened, and is 
divided into three parts, a narrow central area, apparently a continuation of 
the longitudinal ridge passing between the eyes, and a broad, sub-semicir¬ 
cular area on either side. Behind this gently elevated region lies a broad, 
nearly smooth depression, followed by the elevated posterior border. 
The ornamentation of the surface consists of conspicuous, squamiform 
tubercles, which are elongate and most elevated over the anterior portion of 
the shield, but become broader and more triangular posteriorly. They are 
arranged in lines concentric with the margin of the shield or with the most 
prominent features of its contour. Within the orbital ridges these scaly 
markings are comparatively fine, and over the depressed posterior area are 
quite obsolete. 
Other parts of the animal are unknown. 
Observations. The specimen from which the above description is drawn, con¬ 
sists of the intaglio and relievo impressions of a single cephalon. These were 
found in a loose block of fine-grained, olive-gray sandstone, in the town of 
Andes, Delaware county, and are now in the possession of Rutgers College, 
New Brunswick, N. J. The mould of the dorsal surface retains all the details 
of structure and ornamentation in great distinctness and perfection, and the 
