298 MICHIGAN SURVEY, 1908. 



Isle Royale: III, 3, Bulrush Zone at western end of Eock Harbor, 

 Nos. 160, 162. No. 162 occurred in a small creek near its mouth, on a 

 silt and debris-covered bottom at a depth of 3 feet. 



75. Pisidium ahdituni Haldeman. 



Range: "North America, from Honduras, north to Alaska." (Dall). 



Michigan : Generally distributed. 



Isle Eoyale: Not found in 1905. See Report Exped., 1904, p. 98. 



76. Pisidium sp.? 



Isle Royale: Undetermined forms of Pisidium were collected in the 

 following localities: III, 3, Bulrush Zone at western end of Eock 

 Harbor, Nos. 159, 160, 163; V, 5, Tamarack Swamp, No. 237. 



