THE PERMIAN PERIOD 



675 



paneled seas of the Pennsylvanian period, and the Permian faunas 

 were lineal descendants of predecessors occupying the same area. 

 At first, nearly all the species were the same as those of the preced- 

 ing period, and hence difficulty has always been experienced in 



Fig. 463. Marine Permian Fauna, a-f, Cephalopods: a, Medlicottia copei 

 White; b and c, Waagenoceras cumminsi White; d and e, Popanoceras 

 walcotti White, three forms of ammonoids with sutures more complicated 

 than in earlier forms; /, Orthoceras rushensis McCh., one of the last of 

 the orthoceratites. g-j, Pelecypods: g, Pseudomonotis hawni (M. and W.) ; 

 h, Myalina permiana (Swall.); i, Aviculopecten occidentalis (Shum.); /, 

 Sedgwickia topekaensis (Shum.). k, Murchisonia sp., a gastropod. 



