THE DISTRIBUTION OF THE 

 UINIOINID^B IIN AlICHIGAIN. 



This paper is based upon the reports filed in connection 

 with the census of Michigan mollusca, undertaken by the 

 Conchological Section of the Academy, shortly after its or- 

 ganization two years ago. The reports now on file comprise 

 every collection, both public and private, known within the 

 state, and purport to give not only every species represented 

 in these collections, but every locality where they have been 

 collected. Every species known to belong to the fauna of the 

 state, with one exception, is represented by from two to more 

 than one hundred entries. The compilation which has been 

 made from these reports may, therefore, be said to represent 

 accurately the extent of our present knowledge of the fauna 

 of the state and of its distribution. 



The unione fauna of this state is the largest and most 

 varied of any portion of the continent included within the 

 drainage area of the great lakes. Michigan is the only one 

 of the states which lies wholly within the St. Lawrence basin 

 and consequently the only one, whose fauna can be considered 

 as a whole without any of the complications arising from a 

 conflict of political and topographical boundaries. The con- 

 sideration of the origin and distribution of its existing fauna 

 is therefore of great interest and, it is believed, of some 

 scientific importance. 



In the "Review of Our Present Knowledge of the Mol- 

 luscan Fauna of Michigan" which was read before the Acad- 

 emy at its first meeting in December, 1894, there were 

 recognized as belonging to the fauna of the state— of 



Unio 42 species. 



Margaritina, 5 " 



Anodonta, L8 " 



Total 65 



Since that time two species of Unio have been added to 

 the list, while, for various reasons, four species there given 

 have been either dropped entirely or united as varieties or 

 synonyms to other forms. 



Of the Anodontas, while it is probable that in the future 

 the number of recognized species will be considerably reduc- 

 ed, it has been thought that at present two only should be 

 eliminated. 



