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 glabélla 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 lamelle 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 pleural lobe of sev- 
eral thoracic segments were found in association with the heads of this and 
the preceding species that show that the pleuron 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 undescribed. On obtaining a large number of specimens 
in 1882, it was found that the species could be connected with Olenellus 
Howelli, a species founded by Mr. Meek on a single large head from the 
Cambrian at Pioche, Nevada. Ona 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. 
