58 PALEONTOLOGY OF THE EUKEKA DISTRICT. 



Formation and localities. Hamburg shale, in the Widewest Ravine 

 north of Adams Hill, and also from the same horizon a short distance south 

 of the Hamburg mine on the east side of the same canon, Eureka District, 

 Nevada; also at about the same horizon on Pogonip Ridge, White Pine 

 District, Nevada. 



Ptychoparia unisulcatus H. & W. 



Crepicephalus (Loganellus) unisulcatvs Hall & Wliitfield, 1877. Geol. Expl. Fortieth 

 Par., vol. iv, p. 216, pi. ii, figs. 22, 23. 



The types of this species are cited by its authors as coming from the 

 limestone of the Potsdam Group at Eureka, Nevada. It is found associated 

 with P. Haguei, in the upper beds of the Secret Canon shale, opposite the 

 dump of the Richmond mine shaft, Ruby Hill, on the northeast side of the 

 canon, and in the lower portion of the Pogonip Group, northeast of Adams 

 Hill. It also occurs in the lower portion of the Pogonip Group, on Pogonip 

 Ridge, White Pine District, Nevada. 



Subgenus PTEROCEPHALUS Eoemer. 



Ptychoparia (Pterocephalus) occidens, n. sp. 

 Plate ix, iig. 21. 



Glabella and fixed cheeks, when united, irregularly elongate-quad- 

 rangular in outline, exclusive of the postero-lateral limbs; widest across 

 the frontal lobe, and curving in towards the eyelobes; greatest width five- 

 sixths of the length. Glabella broadly conical, rounded in front, and mod- 

 erately convex; marked by a pair of short posterior furrows. 



Occipital ring narrow, rounded, separated from the base of the gla- 

 bella by a narrow, distinct occipital furrow; fixed cheeks rather narrow; 

 palpebral lobes small, and situated opposite the central portion of the gla- 

 bella; frontal limb expanded, its length equaling more than one-third the 

 entire length of the head; concave from the front to the back, and appar- 

 ently without a raised anterior rim; postero-lateral limbs extended, the 

 suture line cutting the posterior margin some distance beyond the line of 



