DBS MOINES ACADEMY OF SCIENCE. 



A GEOGRAPHIC CATALOGUE 



-OF THE 



UNIOMD^E OF THE MISSISSIPPI VALLEY. 



BY R. KLLSWORTH CALL. 



The incompleteness of this first attempt to succinctly present the geographic 

 distribution of the Unionida' of the drainage system of the Mississippi river 

 will be conspicuous to those who may have given the subject any careful study. 

 The causes of such incompleteness are to be referred to the dearth of a special 

 literature and to the absence of complete collections made over all portions of 

 the included area. For the same reason, there may be question whether the dis- 

 tribution of many of the species herein included shall not need future modifica- 

 cation. The states west of the Mississippi river yet remain to be fully searched, 

 and their molluscan fauna carefully studied. Aside from a fragmentary knowl- 

 edge of the shells of Texas, Louisiana, Indian Territory, Kansas and Iowa, 

 almost nothing is known of this area. 



Then, again, the continually recuning problems in synonomy have necessarily 

 modified the statement of the extremes of distribution. It has been difficult to 

 decide just where any individual member of a widely spread group, for example, 

 like that of Unio rubiginosus, ceased and another replaced it. In certain cases 

 the intermingling of closely related forms appears to be indicative of identity 

 rather than of specific distinctness, and it is often a question whether to state the 

 limits of distribution of each form separately or to unite them and point out the 



