CRUSTACEA. 121 



to the pygidium. Segments flat, transverse, or with a gentle forward curve 

 over the axial line. 



Pleura flattened for one-half their width, and thence depressed in a more 

 or less abrupt curve to the margins. Each segmenl is sulcate, the anterior 

 limb being sharply angulated at the fulcrum and becoming rapidly obsolete 

 upon the lateral slope. 



Pygidium sub-semicircular or sub-semi-elliptical in outline, faintly and broadly 

 emarginate behind; length to width as 1 to 2 ; surface depressed-convex. 



Axis broad on the anterior margin ; width equal to one-third the width of 

 the shield ; arched and sloping to a termination within the posterior border, 

 a low ridge connecting the apex of the axis with the margin; composed of 

 nine or ten low, flattened annulations, which have a forward inclination for 

 about one-fourth their width from the axial margins and pass over the median 

 area in a gentle posterior curve. 



Pleura gently depressed, bearing six annulations with indications of a 

 seventh, which are low, flat and faintly sulcate, becoming obsolete at or near 

 the margin. The border is conspicuously thickened and moderately broad. 



Hypostoma with a very convex centrum, sides abruptly depressed and margins 

 flattened. Widest on the anterior margin ; lateral margins incurved ; poste- 

 rior area extended ; posterior sulcus deep ; postero-lateral sulcus conspicuous, 

 elevated. Length equal to the width on the anterior margin. 



Surface Ornamentation. Upon the cephalon the surface of the glabella is 

 covered with faint, obsolete pustules, and most individuals show indications 

 of a large but indistinct tubercle in the axial line at the base of the glabella. 

 The summit of the cheeks beneath the orbital ridges is covered with obscure, 

 elongate or radiating tubercles, interspersed with simple pustules. Upon the 

 thorax and pygidium the posterior edge of each segment and annulation bears 

 a single row of sharply defined granulations; sometimes accompanied by 

 finer and irregularly scattered granules. There are usually indications of a 

 row of faint axial tubercles beginning at the occipital ring, omitting the first 

 six thoracic segments, thence recurring and extending to the second or third 



