CRUSTACEA. 149 



Thorax elongate, length to width as L.3 to 1. Margins tapering with a regular 

 curvature. Composed of twelve segments of which the first, fourth and 

 sixth are the stronger, the last two being spiniferous. 



Axis broad and arched; width equal to one-third that of the thorax; 

 widest at the third or fourth segment and tapering rapidly to the pygidium. 



Pleura, flattened near the axis for about one-third their width, and sharply 

 deflected at the fulcra. Pleural sulci strong; anterior pleural limbs angu- 

 lated by the articulating planes, not becoming obsolete on the lateral slopes 

 as in most species of this genus. Posterior limbs of the pleural segments 

 very strong. 



Pygidium minute ; length to width as 1 to 2. 



Axis broad, tapering rapidly to an obtuse termination within the posterior 

 margin; bearing two strong annulations, with indications of a third. 



Pleura deflected, each bearing three double annulations, which become 

 obsolete within the slightly thickened margin. 



Surface Ornamentation. Cephalon usually pustulose, the pustules being 

 strongest upon the glabella and frontal area. The ornamentation upon these 

 parts is often nearly obsolete, and the frontal margin generally quite smooth. 

 sometimes with scattered obsolete pustules. The occipital ring, and the 

 fourth and sixth segments of the thorax each bear a single slightly recurved 

 spine, that upon the sixth segment being much the strongest On the axis 

 are four rows of minute granules, two on each side of the median line The 

 fulcra of the pleurae each bear a single row of small bead-like pustules. 

 These rows of pustules, upon the axis and pleurae of the pygidium, approx- 

 imate, and the posterior area is covered with scattered granulations. 



Dimensions. An average entire individual measures: 



Body. 



Length 12 mm. 



Width 6.5 mm. 



Fragments occasionally indicate slightly larger dimensions than the above. 



