OR1SKANY FAUNA OF BECRAFT MOUNTAIN 93 



o r t h i s and Hebertella. The upper Siluric genera M i m u 1 u s and 

 Streptis are absent. 



Strophomena has not been perpetuated beyond the Siluric. 



Plectambonites disappears in the Niagaran. 



Of the genus Spirifer, we have no representative of the S . 

 n o b i 1 i s type (Radiati duplicati). 



The genera Whitfieldella, Hyattella, Dayia, Hindella, 

 Meristina, Glassia, Zygospira are absent. 



Rhynchotreta and Parastrophia disappear with the 

 Niagaran. 



Conchidium, Pentamerus, BarrandeJla and Strick- 

 landinia are not present. 



No terebratuloid genus is known in the upper Siluric. 



Eichwaldia disappears with the Niagaran. 



These genera of Crinoids disappear with the Niagaran fauna : 

 Eucalyptocrin us, Glyptaster, Thy sanocrinus, Marsupio- 

 crinus, Lyriocrinus, Lampterocrinus, Lecanocrinus, 

 Pisocrinus, Allocrinus, Coccocrinus, D e n d rocrin u s, 

 Ampheristocrinus: None of the following Niagaran genera of Cys- 

 toids continue beyond that fauna : Caryocrinus, Callocystites, 

 Ly s ocy s tites, Gr o m p h o c y s t i t cs, All ocy s ti t e s, Halocys- 

 tites, Hemicosmites, Apiocystites, Heterocystites. 



This statement of the affinities of the various generic elements of 

 the Helderbergian fauna is more graphically represented as below. 

 The direction of the dashes indicates either (forward) Devonic or 

 (backward) Siluric affinity. 



Trilobites 



Dalmanites (Synphoria) Lichas 



Phacops Proetus 



Homalonotus Cordania 



Bronteus Cyphaspis 



Acidaspis 



Ceplialopods 

 Orthoceras Cyrtoceras 



