THE UPPER SILURIAN PERIOD. 



127 



Trimerellids ; the old and at the same time modern Lingidce, 

 Distinct, and Crania; together jivith many species of Airy fa 



. 68. Upper Silurian Brachiopods. a a', Leptoccelia plano-convexa, Clinton 

 Group, America ; b !>', RhynchoneUa. neglecta, Clinton Group, America ; c, Rhynckonella 

 cnneata, Niagara Group, America, and Wenlock Group, Britain; d d' ', Orthis elegan- 

 tula, Llandeilo to Ludlow, America and Europe; e e , A try fa hemispherica, Clinton 

 Group, America, and Llandovery and May Hill Groups, Britain \ff, Airy pa congesta, 

 Clinton Group, America ; g g' , Orthis Davidsoni, Clinton Group, America. (After Hall, 

 Billings, and the Author.) 



(fig, 68, e), Leptoccelia (fig. 68, a\ RhynchoneUa (fig. 68, b, c), 

 Meristella (fig. 69, a, <?,/), Athyris, Rdzia, C/wnetes, &c. 



. Fig. 69. a, a 1 Meristella intermedia, Niagara Group, America ; I, Spirifera Niagar- 

 ensis, Niagara Group, America ; c c , Spirifera crispci, May Hill to Ludlow, Britain, and 

 Niagara Group, America ; d, Strophomena (Streptorkynchrts) subplana, Niagara Group, 

 America ; e, Meristella navifomiis, Niagara Group, America ;_/, Meristella cylindrica, 

 Niagara Group, America. (After Hall, Billings, and the Author.) 



The higher groups of the Mollusca are also largely repre- 

 sented in the Upper Silurian. Apart from some singular types, 



