CRUSTACEA. 
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to the pygidium. Segments flat, transverse, or with a gentle forward curve 
over the axial line. 
Pleum flattened for one-half their width, and thence depressed in a more 
or less abrupt curve to the margins. Each segment is sulcate, the anterior 
limb being sharply angulated at the fulcrum and becoming rapidly obsolete 
upon the lateral slope. 
Pygidium sub-semicircular or sub-senii-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 oyer the median 
area in a gentle posterior curve. 
Pleum 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 roAV 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 
