FOSSILS OF THE CAMBRIAN. 



31 



in outline, their posterior margin marked by a more or less prominent curve 

 or angle between the genal angle and the inner end of the margin. 



The facial suture cuts the anterior margin some distance outside the 

 line of the outer margin of the glabella and passes obliquely inward to the 

 anterior angle of the eyelobe; curving around the outer margin of this, it 

 passes obliquely outward to the posterior margin, cutting it about midway 

 between the glabellar lobe and the outer margin of the genal angle. 



The surface of the glabella is beautifully ornamented with transverse, 

 fine, irregularly-waving, subimbricating lines that give the appearance of 

 imbricating lamellae resting one under the other from before backward; this 

 feature is only seen on the most perfectly preserved specimens; the surface 

 of the cheeks is slightly granulose under a strong magnifying glass. The 

 test itself is very thin and fragile and is usually broken away. 



Thorax and pygidium unknown. Portions of the plenral lobe of sev- 

 eral thoracic segments were found in association with the heads of this and 

 the preceding species that show that the pletiron is prolonged in all of them, 

 in one more than the others, and that the portions of the segments preserved 

 are typical in their character of the genus; the pleural groove is strong and 

 broad, continuing well out towards the extremity beyond the geniculation. 



The description of the cephalic shield is that of what is considered as 

 the normal, adult type of the head, and omits altogether the phases of this 

 remarkable species that are shown in its various stages of growth and devel- 

 opment. A note and several figures in illustration are appended that were 

 prepared after the first study of the collections. 



The above description was written in 1880 under the impression that 

 the species was nndescribed. On obtaining a large number of specimens 

 in 1882, it was found that the species could be connected with Olemllus 

 Howellij a species founded by Mr. Meek on a single large head from the 

 Cambrian at Pioche, Nevada. On a direct comparison with the type the 

 larger specimens are seen to be essentially the same if we allow for the 

 compression of the Eureka specimens in the sandy shale. 



Formation and locality. Cambrian. Prospect Mountain Group in an 

 arenaceous shale above the quartzite capping the summit of Prospect Peak, 

 Eureka District, Nevada. 



