THE UPPER SILURIAN PERIOD. 



129 



close of the Upper Silurian ; but they are specially character- 

 istic of the May Hill and Wenlock groups, both in Britain 



e 



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

 Group, America; b b', Rhynchonella neglecta, Clinton Group, America; e, Bhynchonella 

 cuneata, Niagara Group, America, and Wenlock Group, Britain ; d d', Orthls elegan- 

 tula, Llandeilo to Ludlow, America and Europe ; e e f , Atrypa fiemispherica, Clinton 

 Group, America, and Llandovery and May Hill Groups, Britain ; ff, Atrypa congesta, 

 Clinton Group. America ; g g', Orthls Davidsoni, Clinton Group, America. (After 

 Hall, Billings, and the Author. ) 



and in other regions. One species, Pentamerus galeatus, is 

 common to Sweden, Britain, and America. Amongst the 



Fig. 69 a, a' Meriitella intermedia, Niagara Group, America ; b, Spirifera Nlagar- 

 enste, Niagara Group, America ; c c', Spirifera crispa, May Hill to Ludlow, Britain, 

 and Niagara Group, America; d, Strophomena (Slreptorhynchiis} subplana, Niagara 

 Group, America ; e, Meristella naviformis, Niagara Group, America ; /, Meristella 

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



remaining Upper Silurian Brachiopods are the extraordinary 

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

 Discing, and Crania; together with many species of Atrypa 

 9 



