ORISKANY FATTKA OF BECRAFT MOUNTAIN 



98 



orthis and Hebertella. The upper Siluric genera Mimulus 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 Whi t f iel d el 1 a, Hyattella, Dayia, Hindella, 

 Meristina, Glassia, Zygospira are absent. 



Ilhyn<jhotreta and Parastrophia disappear with the 

 Niagaran. 



Conchidium, Pentamerus, Barrandella and Strick- 

 land i n i a 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: 

 Eucalyptocrinus, Glyptaster, Thy sanocrinus, Marsupio- 

 crinus, Lyriocrinus, Lamp terocrinu s, L ecanocrinus, 

 Pisocrinus, Allocrinus, Coccocrinus, D e nd rocrin u s, 

 Ampheristocrinus. None of the following Niagaran genera of Cys- 

 toids continiie beyond that fauna : Caryocrinus, Callocystites, 

 Ly socy s tites, G o ra p h o c y s t i t es, Al 1 oc y 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. 



Trilohites 

 Dalmanites (Synphoria) — Lichas — 



Phacops — Proetus — 



-r-Homalonotus Cordania — 



Bronteus — , Cyphaspis — 



Acidaspis — 



Cephalopods 

 — Orthoceras — — Cyrtoceras — 



