ECOLOGY OP ISLE ROYALB. 295 



V, 6, South Shore of Siskowit Lake, Nos. 210, 211, 218; Sargent Lake, 

 No. 112. 



Abundant in all of the lakes, especially on sandy or gravelly bottom 

 in the smaller coves sheltered from the waves. 



57. Anodonta marginata Say. 



Eange: "Drainage of the St. Lawrence River basin, including the 

 Lakes." (Dall). 



Michigan : Generally distributed. 



Isle Royale: II, 1, Benson Brook Clearing, No. 80 A; II, 5, Forbes 

 Lake, No. 90; III, 5, Sumner Lake, Nos. 94, 120, 135, 139, 154, 186, 

 (Wood) ; IV, 3, Bayou at Tobin Harbor, No. 124; V, 6, South shore of 

 Siskowit Lake, No. 210 ; VII, '04, Lake Desor, No. 139 A. 



58.* Sphaerium simile (Say). 



Range: "United States east of the Mississippi River; Canada, Mani- 

 toba." (Dall). 



Michigan : Lake Michigan and Lake Superior. 



Isle Royaile: III, 5, Sumner Lake. Only two immature valves taken. 



59.* SphaeriMm walheri Sterki. 



Range: Lake Michigan and Northward. 



Michigan : Generally distributed. 



Isle Royale: III, 2, Small Island in Rock Harbor, No. 89. A single 

 fragmentary specimen is doubtfully referred to this species by Dr. V. 

 Sterki. 



60.* Mtisciilium securis (Prime). 



Eange: Northern United States, Maine to Minnesota. 



Michigan: Generally distributed. 



Isle Royale: III, 3, Bulrush Zone, Rock Harbor, No. 160; III, 5, 

 Sumner Lake, Nos. 77 A, 78 A, 79, 176; V, 9, Outlet of Siskowit Lake, 

 No. 238. A few examples only of a small form. Some immature ex- 

 amples from the latter locality "may be the same." 



In small, shallow pools in the outlet of Siskowit Lake (No. 238) and 

 at the margin and .Sedge Zone of Sumner Lake (No. 77 A, 78 A). 



61.* Pisidium idahoense Roper. 



Range: Idaho; Washington; Alaska; Lake Michigan; Lake Superior. 



Michigan : Laike Michigan and Lake Superior. 



Isle Royale: III, 2, Small Island in Rock Harbor, No. 89; III, 3, 

 Bulrush Zone, Rock Harbor, Nos. 159, 160. 162, 163. Rather common. 

 The Isle Royale form is similar to that from Lake Michigan and is neither 

 as large nor as inflated as the typical form. 



Dredged from a muddy bottom in 2-5 feet of water at the head of 

 Rock Harbor and in a small stream flowing into it. (Nos. 159, 160, 

 162, 163.) 



62. Pisidium variaMle Prime. 



Range: "Eastern United States, north of Virginia; Colorado and 

 northward." (Dall). 



Michigan: Generally distributed. 



Isle Royale: III, 5, Sumner Lake, 77 A; III, 2, Small Island in 

 Rock Harbor, No. 89; III, 3, Bulnish Zone, Rock Harbor, Nos. 160, 

 162, 163 ; V, 9, Outlet of Siskowit Lake, No. 238. 



With the last at the head of Rock Harbor, and also in the small 



