ORISKAWY FAUNA OF BECBAFT MOUNTAIN 85 



Cyrtoceras are very imperfectly known. The little known species 

 of Cyrtoceras are not diagnostic. 



Pteropods. The species of Conularia and Tentaculites 

 present no diagnostic characters. 



Gastropods. Holopea, Diaphorostoma, Strophostylus 

 are diffused throughout Siluric and Devonic horizons. Of all these 

 genera Holopea alone is near its Siluric culmination. 



Lamellibranclis. Cypricardinia is freely represented in the 

 Niagara!!, but its culmination is of Devonic age. Actiuopteria 

 occurs occasionally in the Niagaran, but its paucity there is in marked 

 contrast to its abundance in the Helderbergian. There are no indub- 

 itably predevonic types in this element of the fauna. 



Bracliiopods. The only species of this extensive group known to 

 be common to the Helderbergian and Niagaran faunas are the cosmo- 

 politan braehiopods, Leptaena rhomboidalis and A t r y p a 

 reticularis. The prevalence of species of Dalmanella is sug- 

 gestive of Siluric affinities. The genus is typically expressed in the 

 species D. elegantula and D. arcuaria of the Niagaran, but attains 

 its culmination in the Helderbergian. (I), planoconvex a, D. per- 

 elegans, D. concinna, D. quadrans). In successive faunas this 

 means no more than the progressive development of a generic group. 

 In time subsequent to the Helderbergian the genus is continued to 

 the close of the Devonic. 



Bilobites varica is foreshadowed in the B. b i 1 o b a and B. 

 acutiloba of the Niagaran. The genus is not of subsequent date. 



Orthostrophia (O. stropho me n o i d e s and O. H a 1 1 i ) rep- 

 resents a short-lived genus, doubtfully anticipated by the Or this 

 fasciata of the Niagaran. 



Scenidium is a genus which appeared in the Trenton, attained 

 its maximum in the Niagaran, declined and disappeared in American 

 faunas with the Sc. insigne of the Helderbergian. In Europe the 

 genus continued into the middle Devonic (Sc. areola Ivays.). 



Of the genus Spirifer the species S. macropleura Con. is a 

 final expression of a group (Hadiati pauciplicuti H. <feC. ) 

 which culminated in the Niagaran. 



