CRUSTACEA. 183 



Nuchal furrow scarcely distinct, its position probably represented by tbe 

 posterior margin of tbe cephalic nodes. 



Cephalic region broadly sub-triangular on each valve, its length about one- 

 third tbe greatest length of the valve. Near the hinge-line is a conspicuous 

 optic node, just behind which lies a low, faintly defined sub-circular eleva- 

 tion, and below this a similar elevation, which is larger, more distinctly 

 defined, oval or more transversely elongate. 



Thoracic region without nodes. Surface ornamented with low tubercles 

 over the cephalic nodes, and with irregularly scattered pustules or granules 

 upon the thoracic area. Fine and elevated, obscurely anastomosing lines 

 are visible near the ventral margin and upon the dorsum, and the postero- 

 ventral margin is distinctly crenulate. 



Abdomen short, composed, as far as known, of two somites, the anterior 

 of which, in the only specimen observed, is partially concealed beneath the 

 posterior area of the carapace. Each one is sub-cylindrical, slightly tapering 

 and gently constricted at the margin, the latter being twice as long as wide. 



Post-abdomen. Caudal plate strongly elevated and wholly occupied by the base 

 of the telson, which is short and stout and bears a conspicuous median ridge. 

 The cercopods are flat, comparatively narrow and longer than the telson, 

 and are minutely crenulated along their inner edges for the attachment of 

 seta?. 



The surface of the abdominal somites and post-abdomen is ornamented 

 with granules and elevated lines. 



Dimensions. The left valve measures 22 mm. in length and 10 mm. in 

 width. The posterior somite of the abdomen measures 7 mm. in length, the 

 telson 9 mm., and each lateral spine 10 mm. in length. 



Distribution. Chemung group. Warren, Warren county, Pennsylvania. 



