Clarke — Crustaceans from the Chemung Group. 



735 



Cephalon. The head is short and subsemilunar in outline, the posterior 

 margin being quite direct. Its length is slightly more than one-halt' its width. 

 The genal angles are somewhat produced into short and broad spines. The 

 margin is elevated, while the border of the head is broadly concave, rising on 

 its proximal limb to a genal ridge. The eyes are small, well back on the 

 cheeks and moderately elevated, the surface between the palpebrum and the 

 dorsal furrows being notably convex. The facial si/tuir* are normal. 

 The glabella is elongate and clavate, its width at the anterior extremity 

 w here it reaches but does not overhang the margin, being twice that just in 

 front of the occipital ring. In contour it is depressed convex, though its 

 elevated median portion attains greater elevation than any other part of the 

 cephalon. The dorsal furrows are deep and narrow ; starting from the 

 posterior margin the}- approach each other rather abruptly ; the curve changes 

 at the level of the posterior part of the eyes and thence forward the furrows 

 diverge outward rather gradually, broadly recurving near the anterior margin. 

 The lateral furrows are short but distinct, the first and third pairs being 

 most clearly defined, a median pair making but a gentle depression upon the 

 surface, w hile the occipital groove is broad and shallow. 



The occipital ring is likewise broad and distinct, but its prolongation to 

 the cheeks is narrower and much more faint. 



In one of the specimens the removal of the part of the glabella has 

 exposed a portion of an elongate hypostome with an oval central depression, 

 surrounded by a narrow regular groove and bordered by a narrow flattened 

 margin. 



Thorax w ith the normal number of ten segments. The axis is very broad, 

 having fully one-third the entire width of the thorax, and its margins curve 

 outward, approaching each other posteriorly. On the axis the segments are 

 moderately broad and flat, distinctly elevated along the median line with 

 genera] longitudinal depressions on the lateral slopes and a slight anterior 

 bend at the sides. On the pleura?, the segments are narrow and soon become 

 free of each other, tapering rapidly to slender, recurved, acute extremities. 



Pygidium semielliptical, flabellif orm ; length and width about equal. 

 Axis very short, extending for not more than one-fifth or one-sixth of the 

 plate; triangular, elevated medially and with an obscure central lobe and 

 depressed lateral slopes. The pleura 1 are broad, flat, separated by sharply 

 defined flat grooves. They broaden rapidly outward and finally become 

 merged into the grooves near the periphery of the plate, so that the margin of 

 the latter is smooth. These ribs are fifteen in number ; the median rib being 



