336 C. R. KEYES 



the various horizons, and for a great succession of abundantly 

 fossiliferous beds in which our published information is meager 

 in the extreme, it is remarkable through how great a vertical 

 interval the main characteristics of this Plattsmouth fauna are 

 preserved. 



The Plattsmouth remains are referred to as forming a charac- 

 teristic maritime fauna. So it is, but it is identically the same 

 fauna that is found at half a hundred other horizons between the 

 lower coal measures and the " Red Beds." Whenever the heavy 

 limestones occur the same groups of brachiopods appear. When- 

 ever the more argillaceous shales are found the same lamelli- 

 branchs begin to predominate. Where the sandstone and 

 coal-bearing shales are prominently developed coal plants and 

 peculiar lamellibranchs and gasteropods are in evidence. These 

 distinct faunas succeed one another in the same vertical section. 

 They are repeated scores of times. Pretty nearly the same 

 phenomena appear to obtain in the great Carboniferous basin of 

 eastern Russia. In both regions the gradual replacement of the 

 brachiopodous fauna by a " Permian " lamellibranch fauna fol- 

 lows the local change of open to closed sea conditions. 



The Permian element of these faunas was merely a shallow 

 water facies of the more typical Carboniferous fauna. It oscil- 

 lated horizontally back and forth with each local change of 

 bathymetric conditions. It was repeatedly intercalated between 

 horizons carrying the greater thalassic phase. Meek's conten- 

 tion for the fauna of the Plattsmouth beds was for its identity 

 with the fauna of the upper coal measures of the region. He was 

 right. In his argument for the Permian character of the same 

 fossils Geinitz was not wholly wrong.* The point of vantage of 

 each was merely slightly different. Could they have consulted 

 more fully, they would have been no doubt soon in close agree- 

 ment. 



TAXONOMIC RANK, OF THE PERMIAN 



Principles of geological classification. — It is a well-known fact 

 that the modern classifications of animals and plants are based 

 primarily upon genetic relationship. A natural arrangement of 



