CAMBRIAN TRILOBITHS — WALCOTT I7 



a narrow thread-like ridge ; the pleiine terminate in falcate extremi- 

 ties, some of which, on the two anterior segments, appear to have a 

 verv short, fine spine at the posterior termination of each pleura. 



Pygidium a narrow, elongate, moderately convex, central plate 

 without defined segments or pleural lobes ; it has a small node at the 

 anterior third of its length. None of the specimens show the pos- 

 terior margin ; it may have been a single, broad spine or it may have 

 terminated with a slightl\" arched posterior margin. 



The outer surface of the dorsal shield appears to have been 

 minutely granular or smooth. 



Dimensions. — The most perfect specimen of the dorsal shield has 

 a length of 7 mm. ; greatest width, 5 mm. The other dimensions are 

 as follows : 



Cephalon : nii;i 



Length 2 . 25 



Width at posterior margin 4-74 



Thorax : 



Length 1 . 75 



Greatest width 5 . 00 



Axial lobe, greatest width i . 50 



Pleural lobe, greatest width i . 75 



Pj'gidium : 



Length to line of contour of dorsal shield i .50 



Width at anterior end 75 



Observations. — This interesting trilobite has a cephalon much 

 like that of Schiiwloisecia amphiomira Moberg,^ but it dififers in de- 

 tails, and the pygidium is quite unlike that of Dr. Moberg's species ; 

 the furrows and ridges on the pygidium of the latter are very similar 

 to those of the thorax of Bitrlingia. 



The stratigraphic horizon of this species is 2,400 feet above the 

 Lower Cambrian or Olenellus fauna and 2,600 feet below the Upper 

 Cambrian fauna. It is associated with Zacanthoidcs spiiwsus, Ogy- 

 gopsis klotzi, Oryctocephalus rcynoklsi, Bathyuriscus rotundatns, 

 Bathyiiriscus oniatus, and other species of the Ogygopsis kJotzi 

 fauna of ]\Iount Stephen. 



The specific name is given in recognition of Sir James Hector, the 

 Canadian geologist and explorer who discovered the Hector or 

 Kicking Horse Pass in 1858. 



Formation and Locality. — Middle Cambrian: Ogygopsis shale 

 of the Stephen formation, 2,400 feet (731.5 m.) above the Lower 



^ Moberg, 1903, Meddelande fran Lunds Geol. Mineral. Inst. No. 5 (Geol. 

 Foren. i Stockholm Forhandlingar, Bd. xx\^ Haft 2, 1903, No. 219), pi. iv, figs. 

 I and 2. 



