78 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



Platycolpus bilobatiis Walcott, Smithsonian Misc. Coll., vol. 57, No. 13, p. 349, 



1914. 

 Pterocephalina bihbata Resser, ibid., vol. 97, No. 10, p. 42, 1938. 



Additional specimens of this species are figured in order that it 

 may be better understood. A small tail is figdred to show the features 

 at that stage. The large cranidium, from which a rim of unknown 

 but evidently considerable width has been broken away, is tentatively 

 assigned to the species. 



Secret Canyon shale; (loc. 65) east side of Sierra Canyon, opposite 

 Pinnacle Peak; and (loc. 61) south of Hamburg Mine, Eureka 

 District, Nevada. 



Holotypc. — U.S.N.M. No. 24568; plesiotypes, Nos. io8782a-c. 



PTEROCEPHALINA POGONIPENSIS, new species 

 Plate 15, Figures 1-2 



Several small pieces of very fossiliferous limestone contain a 

 pygidium and a cranidium regarded as belonging to the same species. 

 Originally it was identified as P. flahcllifcr. 



The cranidium is small for the genus. The glabella occupies more 

 than half the cranidial length and since it is exfoliated, three pairs of 

 recurved furrows are faintly visible in cross light. The concaA^e brim 

 is divided into a slightly convex preglabellar area and a wider, flat, 

 somewhat upturned rim. The convex fixigenes are less than half the 

 glabellar width. 



As may be observed in the illustrations the axis occupies nearly 

 the full length of the pygidium. It is almost straight on top, sloping 

 back at an even rate to the short postaxial ridge. Axial and pleural 

 furrows are well developed, the latter extending to the margins. 

 Though the lateral margins are somewhat extended, the border is less 

 flared than in more typical species. 



Secret Canyon shale ; west side of Pogonip Mountain, White Pine 

 District, Nevada. 



Holotype. — U.S.N.M. No. 108783a; paratype, No. 108783b. 



PTEROCEPHALINA GRATA, new species 

 Plate 15, Figures 3-6 



This small distinctive species is represented by several cranidia and 

 pygidia. The narrow cranidium has a large slightly tapered glabella 

 and a concave brim about one-third as wide as the glabellar length. 

 The demarcation of a wide rim is so faint that only in a certain light 

 docs the brim appear to be anything but a simple concave plate. 



