0RI8KANY FAUNA OF BECRAFT MOUNTAIN 85 



Cyrtoceras are very imperfectly known. The little known species 

 of Cyrtoceras are not diagnostic. 



Pteropods. The species of Conularia and Tentacnlites 

 present no diagnostic characters. 



Gastropods. Holopea, Diaphorostorna, Strophostylus 

 are diffused throughout Siluric and Devonic horizons. Of all these 

 genera H o 1 o p e a alone is near its Siluric culmination. 



Lamellibranehs. Cypricardinia is freely represented in the 

 Niagaran, but its culmination is of Devonic age. Actinopteria 

 pccurs 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. 



Brachiopods. The only species of this extensive group known to 

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

 politan brachiopods, Leptaena rhomboidalis and A try pa 

 reticularis. The prevalence of species of Dalmanella is sug- 

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

 species D. elegant u la and D. arcuaria of the Niagaran, but attains 

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

 e 1 e g a n s, D. c o n c i n n a, 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. s t r o p h o me n o i d e s and O. H a 1 1 i ) rep- 

 resents a short-lived genus, doubtfully anticipated by the O r t h i s 

 f a s c i a t a of the Niagaran. 



S c e n i d i u m is a genus Avhich appeared in the Trenton, attained 

 its maximum in the Niagaran, declined and disappeared in American 

 faunas with the Sc. in sign e of the Helderbergian. In Europe the 

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



Of the genus Spirifer the species S. m a c r o p 1 e u r a Con. is a 

 final expression of a group (Hadiati pauciplicati H. <&0. ) 

 which culminated in the Niagaran. 



