OF CENTRAL CANADA PART IV. 



269 



Spiriferidce ; 2, Atrypidce, ; 3, Terebratulidce ; 4, RhynconellidoR ; 5, 

 Strophomenidce ; 6, Produetidce. 



Family 1. Spiriferidce : Shell with both valves convex. Smaller 

 valve with internal calcareous spires, tapering laterally. 



The principal genera of Canadian occurrence comprise : Spirifer, 

 with straight hinge-line, and beaks comparatively near together (Sil- 

 urian to Lias) ; figures 183, 184, 185. Cyrtina, with straight 

 hinge-line and large area, the beaks consequently far apart (Silurian 

 to Trias) ; fig. 186. And Spirigera (or Athyris), with curved hinge- 

 line; Silurian to Trias); fig. 187. 



184 bin. 



184. 



183. 



185. 



Fig. 184 bis. S. gregarius 



Fig. 183. Interior of dorsal 

 valve of a spirifer shewing posi- 

 tion of spiral arm-supports. 



Fig. 184. S. radiatus: Ni- 

 agara Formation. 

 Corniferous (Devonian) Formation. 



Fig. 185. S. mucronatus : Devonian. 



Fig. 186. Cyrtina. Devonian. 



Fig. 187. Spirigera (Athyris) concentrica : Devonian. 



Note :The Spiriferidce, in accordance with their more prominent characters, may be 

 grouped in two sections and four sub-sections, as follows : 



1. Librati : Hinge-line straight. A distinct area : 



A. Vicinale* : Beaks near together ; Type-forms : Spirifer, Spiriferina. 



B. Disjuncti: Beaks widely apart ; Type-forms: Cyrtia, Cyrtina. 

 2. Arcuati : Hinge-line curved. True area, absent or indistinct. 



A. Vicinales : Beaks near together ; Type-forms : Spirigera ( = Athyris) 



Retzia. 



B. Disjuncti: Beaks widely apart ; Type-form: Uncites. 



