126 Trans. Acad. Sci. of St. Louis. 



only in Belgium from near the base of the Carboniferous. 

 Avicula is in general a later genus. Not only are most of the 

 genera of pelecypods abundantly represented in the Devo- 

 nian, but in several instances the species in the Chonopectus 

 sandstone are so nearly like species in the Chemung of New 

 York, that it is largely a matter of personal opinion as to 

 whether they are really distinct or not. These specific simi- 

 larities have been pointed out in connection with the descrip- 

 tions of the species. 



The gastropods and cephalopods are also, for the most 

 part, of Devonian types, with no strikingly Carboniferous 

 characteristics. The genus Agoniatites has not previously 

 been recognized outside the Devonian, and Orthoceras whitei 

 is a very ancient type, being related to the Silurian 0. annu- 

 latum. 



Taken as a whole, a larger number of the total 81 species 

 recognized in the fauna, have Devonian and not Carbonifer- 

 ous relationships, but this is not sufficient evidence upon which 

 to establish the Devonian age of the fauna. In general, in 

 paleontologic interpretation, the initiation of a new inverte- 

 brate faunal element is of greater importance than the hold- 

 ing over of a much larger element from an older fauna, and 

 on this principle the strongly Carboniferous element among 

 the brachiopods of the Chonopectus sandstone is to be consid- 

 ered as weightier evidence than the holdover pelecypods and 

 cephalopods. 



In the interior of the North American continent, the divid- 

 ing line between the Devonian and Carboniferous periods is 

 not sharply defined like that between the Ordovician and Silu- 

 rian, for instance, but judging from the association of genera 

 and species alone, the fauna under consideration, and indeed 

 all the Kinderhook faunas, should be placed in the Carbonif- 

 erous. However, if it can in any way be demonstrated that 

 the strong Carboniferous element in the fauna had its point of 

 origin right here in the Mississippi valley, and that these types 

 of life existed here earlier than in any other part of the world, 

 their presence in other regions being due to migrations of life 

 from this region, then there may be some foundation for con- 

 sidering a part or the whole of the Kinderhook as being the 



