NO. 5 CAMBRIAN TRILOBITES 387 



pairs of glabellar furrows, which can only be seen where the surface 

 is very perfectly preserved. Occipital ring about as wide as the 

 frontal margin and separated from the glabella by a shallow furrow 

 that terminates on the side slightly in advance of the posterior intra- 

 marginal furrow. Free cheeks about as wide opposite the eye as the 

 fixed cheeks ; eye lobe about one-fourth the length of the cephalon. 

 Postero-lateral angle continued backward into a moderately strong 

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

 genal ang-le 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 fiat out to the 

 geniculation, 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 con- 

 tinued 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 1 1 .0 



Length of eye-lobe . 3.5 



Width at posterior margin 20.0 



Width of glabella at posterior margin 6.0 



