THE UPPER SILURIAN PERIOD. 



129 



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

 istic of the May Hill and \Yenlock groups, both in Britain 



Fig. 68. Upper Silurian Brachlopods. a a', Leptoccelia piano- convexa, Clinton 

 Group, America; & &', Rhynchone.Ua neglecta, Clinton Group, America; c, Rhynchonella 

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

 tula, Llandeilo to Ludlow, America and Europe ; e e', Atrypa hemispherica, Clinton 

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

 Clinton Group, America;^ g', Orthis 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' Merittella intermedia, Niagara Group, America ; 6, Spirifera Niagar- 

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

 and Niagara Group, America; d, Strophomena (Slreptorhynchus} 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 Lhn/ulic, 

 Discina, and Crania; together with many species of Atrypa 

 9 



