18 PREFACE. 



tions. The most characteristic forms of the various geological 

 horizons, and the species which are little known, have been 

 considered more in detail than other forms equally interesting 

 and perhaps even more important. Certain large groups have 

 consequently been very briefly alluded to. Such are the 

 Polyozoans, Vertebrates, and various sections holding lower 

 taxonomic ranks. For the determination of the geological age 

 of rocks, the Polyozoans are practically of no value to the 

 average citizen of the State. This class has therefore received 

 but little study in the present connection — only the more 

 important species being described, though a considerable num- 

 ber of other species are listed which have been reported from 

 localities on the boundaries of Missouri in adjacent states. 



The detailed discussion of the general stratigraphy of 

 Missouri must be reserved necessarily for another time. In 

 the present connection merely a brief stratigraphical outline 

 is given, in order that the geological relations of the fossils 

 may be more readily comprehended. Although many interest- 

 ing facts relating to this subject have been brought to light 

 during the prosjress of the present investigation, it has been 

 thought best not to present them until other equally important 

 problems have been solved, and then bring the whole together 

 in a comprehensive treatment of the entire subject. The 

 memoir is therefore practically a synopsis of the fossil remains 

 at present known from the State; and in most cases the spe- 

 cific details have been necessarily confined mainly to short 

 comparisons, usually in pointing out the diagnostic characters 

 of each species. 



Sincere thanks are tendered to Mr. Arthur Winslow, the 

 late director of the Missouri Geological Survey, for the many 

 kind attentions and suggestions which added zest and pleasure 

 to the work during its early progress, and for freely offering 

 every facility possible for the advancement of the report. 



Special acknowledgments are also due : Dr. John H. Britts, 

 of Clinton, who, for many years, has done much to advance 

 paleontology by collecting large numbers of our coal plants, 

 many new to science, and who, with one or two others, has 



