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 toa 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. 
