CAMBRIAN TRILOBITES- — WALCOTT 3/ 



Thorax with seven segments ; axial lobe convex, and as wide as 

 the pleural lobes exclusive of the terminal spines ; a strong, short, 

 sharp spine occurs at the center of each segment, and a narrow, 

 transverse, low, rounded ridge on each side next to the dorsal 

 furrow ; the pleural lobes are slightly convex ; each pleura has a 

 strong, diagonal furrow that originates near the front margin next 

 to the dorsal furrow and gradually widens toward the outer end, 

 where it terminates nearly at the center of the pleura and within 

 the base of the sharp, terminal spine ; a narrow, rounded ridge occurs 

 on each side of the pleural furrow that forms the margins of the 

 pleur?e ; the terminal spines have a broad base and extend obliquely 

 outward and slightly backward a short distance. 



Pygidium large, moderately convex; anterior margin nearly 

 transverse and posterior outline semicircular ; axial lobe convex, a 

 little shorter than the entire length ; it is divided into seven rings 

 and a terminal section by seven nearly transverse, narrow furrows ; 

 a low, narrow median ridge is indicated by the termination of the 

 deeper portion of each transverse furrow just outside of the median 

 line ; five anchylosed pleural segments are outlined on the pleural 

 lobes on each side of the axial lobe ; the furrows all terminate 

 within the slightly flattened, rounded border, which has five straight, 

 narrow spines extending out from it on each side ; the anterior 

 segment of the pygidium is so much like the segments of the thorax 

 that it is difiicult to distinguish it from the thorax. 



Hypostoma similar to that oi Neolenus inflatus, except that its 

 body is less convex, and small specimens show an elongate tubercle 

 on each side just back- of the line separating the convex body from 

 its posterior, Tess convex, and narrower portion. 



Surface with variously arranged, irregular, short, very fine, 

 raised lines or minute ridges ; on the glabella they are arranged 

 in a concentric manner, although very irregular and interrupted by 

 numerous breaks in continuity and strength ; on the cheeks the lines 

 are somewhat coarser ; on the thorax and pygidium the lines are 

 exceedingly fine and inconspicuous ; where seen they have about the 

 same arrangement as those of the surface of Neolcnns inflatus. 



Dimensions. — A dorsal shield 65 mm. in length has the following 

 dimensions : 



Cephalon : mm. 



Length 23 . 00 



Length of glabella 17.00 



Length of eye lobe 2 . 75 



Width at base 38.00 



Width of glabella at posterior margin 12.00 



Width of glabella at anterior end 13.50 



