Bull. U. S. H. 1"., 1919-20. 



Pl.ATI- X. 



Fl'".. 1 . — I..n\ H r 1' ri : ';i 'A < ■: ni'l RiviT. Mich . 



i'-i'.i :;^u:ial (.uiidUiuii- 



TiG. J.— I.uwtr purliuii uf Grand River where conditions have been rendered un.suiluble fur mussels by 

 canalization in interest of navigation. 



