lOO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 5/ 



spine. The facial sutures cut the posterior margin just within the 

 genal angle and extend obliquely inward with a slightly sigmoid 

 curvature to the base of the eye lobes ; curving over and around the 

 eye lobes, they pass forward and a little outward, cutting the frontal 

 margin obliquely. 



Thorax with nine segments ; axial lobe moderately convex, slightly 

 narrower than the pleural lobes in compressed specimens ; on the 

 outer side of each segment a low rounded node or ridge is separated 

 from the main body of the segment by a slightly oblique furrow 

 transverse to the segment; pleural lobes slightly convex, nearly flat 

 out to the geniculat'ion where they curve slightly downward and 

 backward ; each pleura has a well-defined furrow starting near the 

 inner anterior margin and extending backward to the center of the 

 pleura at the geniculation, where it curves slightly backward and 

 terminates on the broadly rounded, slightly falcate end of the pleura. 



Pygidium roughly semicircular in outline, one-fourth the length 

 of the dorsal shield ; anterior margin nearly transverse at the axial 

 lobe and curving slightly backward to conform to the curvature of 

 the last thoracic segment ; axial lobe moderately convex and tapering 

 gradually toward its posterior section which is just within the nearly 

 flat marginal border ; it is divided by four transverse furrows into 

 four rings and a terminal section ; three anchylosed pleural segments 

 are outlined on the pleural lobes by furrows that curve backward 

 and terminate on the inner margin of the doublure ; this line is 

 continued forward on the pleural lobes of the thorax, terminating on 

 each side opposite the posterior end of the facial suture. 



Surface of specimens preserved in the limestone nearly smooth 

 or marked by very minute shallow pits. 



Dimensions. — A dorsal shield 30 mm. in length has the following 

 dimensions : 



Cephalon: mm. 



Length ii.o 



Length of eye lobe 3.5 



Width at posterior margin 20.0 



Width of glabella at posterior margin 6.0 



Thorax: 



Length 12.0 



Width at fourth segment 19.0 



Width of axial lobe at first segment 5.5 



Width of axial lobe at ninth segment 4.0 



Pygidium : 



Length 7.0 



Width at union with thorax 12.0 



