INTRODUCTORY NOTE. 



The specimens described in this paper were collected by the 

 writer at different times while studying the geological formations of 

 Kansas. The Ft. Pierre fossils were collected from the deposits bear- 

 ing that name in the extreme northwestern part of the State. The 

 Benton fossils were obtained from outcrops of that formation in the 

 central part of the State, in Osborne, Lincoln and Mitchell Counties. 

 The Niobrara species were collected from outcrops on the Smoky 

 Hill river in Ellis County, and from outcrops on the White Rock in 

 Jewell County. 



Some of the Benton forms, particularly the gastropods, were 

 taken from calcareous nodules which were so thoroughly indurated 

 that the shell could not be obtained in a form complete enough to 

 warrant specific determinations. Nevertheless, they are figured and 

 the best description possible from the material is given. The remain- 

 ing specimens are well preserved. 



A comparison of some of the species of the same genus led the 

 author to a study of the distribution, ontogeny, and phylogeny of 

 some of the genera. The results of this study are included in the 

 present paper. 



The specimens treated of in this paper are now in the paleonto- 

 logical collection of the Field Columbian Museum. 



