CRUSTACEA. L59 



orbital ridge. These ridges slope gradually outward, bul more abruptly on 

 their inner faces, their anterior extremities approximating tbe 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, eoarselv tuhercled 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 



