BRACHIOPODA. 



445 



rocks younger than the Lias. Of the genera of the family, 

 the most important is the genus Spirifera, or Spirifer (fig. 

 286), in which the valves are articulated by teeth and sockets, 

 and the shell is not punctated. The hinge-line is long and 

 straight, and the well-marked hinge-area is divided across in 

 each valve by a triangular fissure, which in the ventral valve 



Fig. 285. Spirifera sculptilis. 

 Devonian. 



Fig. 286. Spirifera mucronata. 

 Devonian. 



is closed more or less completely by a pseudo-deltidium, and 

 in the dorsal valve is occupied by the cardinal process. The 

 true Spirifers are mainly Upper Silurian, Devonian, and Car- 

 boniferous, and the forms of the second of these formations 

 often have the shell winged, or drawn out at the lateral 

 angles (fig. 286). In the Permian rocks a few species of 



Fig. 287. Spirifera Nia- 

 garensis. Upper Silurian, 

 America. 



Fig. 288. Spiriferina ros- 

 trata. Lias. 



Fig. 289. Spirifera tri- 

 gonalis. Carboniferous 

 Limestone. 



the genus are found. If it be admitted that the possession 

 of a non-punctated shell is an essential characteristic of the 

 genus Spirifera, then no forms of this type have as yet been 

 detected in deposits younger than the Palaeozoic. We meet, 

 however, in the Lias (Jurassic) with several forms (fig. 288) 

 which agree in other respects with Spirifera proper, but 

 which possess a punctated shell. These forms, along with 

 others from the Carboniferous and Devonian, are now placed 

 in the genus Spiriferina, which is separable from Spirifera 



