24 INTRODUCTION. 



ginally brought into public uotice, the type specimens have 

 passed through many vicissitudes ; some have been irretrieva- 

 bly lost ; some ha^e had their labels destroyed and now are 

 mixed up indiscriminately with other material ; and still others, 

 if they exist at all, are totally inaccessible. It is with extreme 

 difiSculty, therefore, that many of these early recognized species 

 can be identified with certainty. Collections from the type 

 localities have removed all doubt in a goodly number of cases. 

 In many instances species have been described from fragmen- 

 tary material, and to a large extent can be ignored. Concern- 

 ing a few of the species, however, doubt will always exist as to 

 their true generic and specific affinities. With these little can 

 be done except to arrange them among the spurious and doubt- 

 ful forms. Most of the fossilfs described from the State in the 

 official reports of neighboring districts and in the various 

 scientific magazines are fully represented in the collections 

 examined ; while a large number of the species here annotated, 

 though already recognized elsewhere, have not until now been 

 recorded from Missouri. 



Studies relating to fossil faunas, taken as a whole, have 

 lately assumed very great importance in the correct interpret- 

 ation of stratigraphical problems. Heretofore the great hin- 

 drance to considerations of this kind has been the chaotic 

 condition of the nomenclature of species, and the multiplica- 

 tion of names for forms already well known. By a careful 

 consideration of the questions of synonymy, a firm basis for 

 invaluable faunal deductions will have been laid, and the com- 

 plex, little understood phases of stratigraphy better made out. 

 Not until all the described forms have passed carefully in 

 review, and their genetic relationships determined with some 

 degree of exactness, can faunal investigations acquire the full 

 consideration they are entitled to ; for under the circumstances 

 which have long existed, any approach to unanimity of opinion 

 regarding the distribution of species in time and space has 

 been difficult to secure. 



Fossils are of interest from three points of view : ( 1 ) bio- 

 logical, { 2 ) geological, and (3) economical. The first two are 



