CLASSIFICATION OF THE MISSISSIPPIAN SERIES 31 1 



exhaust the vitality. While the close struggle for existence 

 between individuals does seem to be a means of bringing about 

 many minor differentiations of specific importance, the more 

 important differentiations of generic or higher rank seem to be 

 associated with conditions under which there is a wealth of 

 resources, where the struggle is between the organism and the 

 physical environment to a greater extent than between organ- 

 isms and their nearly related fellows. 



The characteristic features of the Osage fauna were assumed 

 at its beginning. After this the struggle was to a greater extent 

 between individuals, and the organic changes were of minor 

 importance, being to a great extent of no more than specific 

 rank. 



That the influence exerted by the American fauna upon 

 that of western Europe was greater than the influence of 

 the European upon the American fauna, is shown by a com- 

 parison of the crinoidal elements of the faunas in the two 

 regions. In the Osage faunas of America 50 genera of crinoids 

 are recognized, and in the equivalent faunas of western Europe 

 21 genera. Of the European genera not a single one is peculiar 

 to the region, each being also represented in America. On the 

 other hand 29 genera are peculiar to the American fauna. 

 Furthermore, of the genera which occur both in America and 

 in Europe, a larger number of species are known in America 

 than in Europe. These facts seem to show that as between the 

 two the point of origin or of major distribution of this crinoidal 

 fauna was in the continental interior province of America, and 

 that in the course of its existence it probably migrated from 

 this province into other regions. 



During the time when the broad expanse of the clear waters 

 of the Osage sea was the most conspicuous feature of North 

 America, there were in existence at least two other and smaller 

 geologic provinces in which different physical conditions pre- 

 vailed, and which were inhabited by very different assemblages 

 of organisms. The first of these, the Waverly, lay to the east 

 of the Osage province, between the Cincinnati island and the 



