BRACHIOPODA. 



453 



especially in the first of these ; but the genus is not known 

 to have survived the ' Carboniferous period. This genus is 



Fig. 302. Lower Silurian Brachiopods. a and a', Orthis Uforata Llandeilo-Caradoc, 

 Britain and America ; 6, Orthis flabellulum-Ca.ra(ioc, Britain ; c, Orthis subqwdmta Cincin- 

 nati Group, America ; c f , Interior of the dorsal valve of the same ; d, Strophomena deltoidea 

 Llandeilo-Caradoc, Britain and America. (After Meek, Hall, and Salter.) 



one of the most important and widely distributed groups of 

 Palaeozoic Brachiopods, and the species belonging to it may 



Fig. 303. Lower Silurian Brachiopods. a, Strophomena alternata Cincinnati Group, 

 America ; b, Strophomena filitexta Trenton and Cincinnati Groups, America ; c, Orthis testu- 

 dinaria Caradoc, Europe and America ; d, d f , Orthis plicatella Cincinnati Group, America ; 

 e, e', e", Leptcena sericea Llandeilo-Caradoc, Europe and America. (After Meek and Hall, 

 and original.) 



generally be recognised from the closely related Strophomence 

 by the fact that the shell is seldom flat, one valve being 



