CRUSTACEA. 
183 
Nuchal furrow scarcely distinct, its position probably represented by the 
posterior margin of the cephalic nodes. 
Cephalic region broadly sub-triangular on each valve, its length about one- 
third the 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 
setae. 
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. 
