CAMBRIAN TRILOBITES — WALCOTT 2/ 



palpebral lobe, and the second pair about half way between them 

 and the outer ends of the posterior pair ; on some specimens a fourth 

 pair is faintly defined on the large anterior lobe close to the dorsal 

 furrow opposite the rounded angle formed by the sides and rounded 

 front of the glabella. Occipital ring strong, rounded, broadest at 

 the center, and narrowing gradually toward the ends ; marked by a 

 small central node near the posterior margin and a rounded, small, 

 depressed tubercle at about one-half the distance between the central 

 node and the dorsal furrow ; occipital furrow distinct, narrow, and 

 nearly transverse. Free cheeks large, body gently convex, and 

 rising from the interborder furrow to the base of the elongate, low 

 eye lobe. The facial sutures cut the posterior margin just outside 

 of the intergenal spine and, curving abruptly inward, extend to the 

 posterior base of the eye lobe ; arching over the latter, they extend 

 forward and slightly outward with a gentle sigmoid curve, so as to 

 cut the outer margin at a distance from the median line of the 

 cranidium equal to the width of the glabella. 



Thorax with nine segments ; axial lobe convex, a little wider than 

 the pleural lobes exclusive of the spinose terminations of the 

 pleurae ; a small elongate node occurs at the center on the posterior 

 half of each segment, except on the fifth, which has a long, slender, 

 backward-extending spine ; on each side, about half way between 

 the center and the dorsal furrow and nearest the anterior margin, 

 there is a rounded, low tubercle, and on the more perfectly preserved 

 specimens a low, rounded, transverse ridge on each side next to the 

 dorsal furrow ; pleural lobes slightly convex ; each pleura has a 

 strong furrow that is broad at the inner end next to the dorsal 

 furrow, from whence it narrows gradually to its sharp extremity 

 near the posterior outer end of the pleura just within the base of 

 the terminal spine; a rovmded, elongate, subtriangular tubercle 

 occupies much of the broad inner end of the furrow ; the front 

 border of each pleura is narrow next to the dorsal furrow ; it grad- 

 ually widens toward the outer end and terminates in a strong, long, 

 backward-extending spine ; the narrow posterior border merges into 

 the base of the terminal spine ; in most specimens the backward 

 curvature of the anterior margin of the pleura is so abrupt that an 

 obtuse angle is formed, while in some the margin curves gradually 

 into the terminal spine. 



Pygidium of medium size ; axial lobe convex, narrow, broader 

 than the pleural lobes, divided by narrow, transverse furrows into 

 four rings and a terminal section that, in large specimens, has a 

 slight, transverse furrow that delimits a fifth narrow rins: ; on the 



