CRUSTACEA. 87 



behind the ocular node, and widening toward the genal angles. Occipital 

 ring strongly arched over the very narrow axis. 



Cheeks, as far as known from a single fragment, relatively broad, evenly 

 rounded upon the margin, and produced at the angles beyond the posterior 

 margin of the shield. 



Thorax. A single detached segment lias been observed, which is strongl} 

 arched upon the axis and slopes rapidly upon the pleura; to the lateral 



margins. It is very narrow and shows no articulating plain's toward the 

 extremities. 



Pvgidium relatively large, rlabellate, depressed-convex. 



Axis less than one-third as wide as the shield upon the anterior margin, 

 strongly arched upon the first two annulations, becoming depressed poste- 

 riorly, tapering to an obtuse termination just below the center of the 

 pygidium and connected with the posterior margin by an elevated ridge. 

 It bears three distinct annulations and seven transverse rows of pustules. 



The pleura are broad, flattened above, and somewhat abruptly deflected 

 near the margins; bearing two distant, elevated, narrow annulations, each of 

 which terminates on the margin in a short spine directed posteriorly. There 

 is no evidence of other annulations upon the pleura?, but the postero-lateral 

 margin bears two other pairs of spines, making in all eight spines in the 

 marginal fimbria. Border thickened, narrow upon the sides, becoming wider 

 at the posterior extremity. 



Surface ornamented with pustules which, on the cephalon, are line and 

 crowded upon the frontal portions and coarser toward the occipital ring. 

 Upon the thorax these pustules appear to he arranged in a single row for 

 each segment. The annulations of the pygidium each hear a single row. 

 and the postero-lateral area is covered with scattered tubercles and granules. 



Dimensions. Average specimens afford the following measurements: 



Cephalon. Hum. 



Length 6 mm. 9 mm. 



Width 6 mm- (between the eyes.) 11 mm. 



