OLENELLUS AND OTHER GENERA OF MESON ACID^ 315 



lobe, strongly granular surface, and strong intergenal and genal 

 spines distinguish it from all known species. In its small palpebral 

 lobes and tendency to develop abnormal forms [pi. 40, fig. 14] O. 

 argcntiis resembles frcmonti [pi. 37, figs. 9-1 1]. The shagreen 

 granulated surface is shown by fig. 16, and the occipital ring with 

 its short, sharp, median spine by fig. 15. The pointed surface granu- 

 lations have a tendency to group in lines on the genal spines, but 

 on the cheeks and glabella there is little trace of systematic arrange- 

 ment. My impression of this surface is that it was formed by the 

 cutting into sections, by transverse furrows, of the irregular net- 

 work of ridges so characteristic of the surface of most species of 

 the Mesonacidse, this process finally forming a large number of 

 sharp isolated granules. 



The strong genal spines and thick outer border of the cephalon are 

 more nearly similar to those of Peachella iddingsi [pi. 40, figs. 17] 

 than any other species. The generic reference is doubtful, and will 

 remain so until more is known of the elements of the thorax and 

 pygidium. 



The stratigraphic horizon of this species is over 1,000 feet higher 

 in the Barrel Spring section of Nevada than the horizon of Olenclhis 

 frcmonti and 0. ? claytoni. The associated fossils are: 



Archcrochyathiis ? . 



Kntorglna cingulata (Billings). 



Kiitorgina perngata Walcott. 



Siphonotreta ? diibia, n. sp. 



Szvantonia zveeksi Walcott. 



Swantonia ? sp. 



Stenothcca cf. elongata Walcott. 



Stenotheca cf. rngosa Walcott. 



Ptychoparia sp. 



IVanncria ? gracilc new species. 



Formation and Locality. — Lower Cambrian: (iv) shales of 

 No. 3 of the Silver Peak Group, Barrel Spring section [Walcott, 

 1908^^ p. 189], 3 miles (4.8 km.) north of \'alcalda Spring, and 4 

 miles (6.4 km.) west-northwest of the Drinkwater Mine, Silver 

 Peak Quadrangle, Esmeralda County, Nevada. 



