292 MICHIGAN SURVEY, 1908. 



41. Physa sp? 



Isle Royale: II, 1, Benson Brook, No. 149, 167; III, 2, Island at 

 West end of Rock Harbor, No. 89; II, 3, Bulrush Zone at western end 

 of Eock Harbor, Nos. 161, 162, 163, 164; North shore of Rock Harbor, 

 No. 110; III, 5, Sumner Lake, Nos. 77 A, 78 A', 79 A; IV, 5, Neutson's 

 Resort at Eock Harbor, No. 44 A; IV, 6, Island in Tobin Harbor, No. 

 123 ; IV, 7, Head of Tobin Harbor, No. 127 ; V, 1, Beach near Siskowit 

 Bay, No. 200; V, 6, South shore of Siskowit Lake, Nos. 220, 221; V, 

 9, Outlet of Siskowit Lake, No. 238; V, 11, Swamp near Siskowit Bay, 

 No. 126 A. 



Under this head are included nearly all the Physw from the harbors 

 and interior waters which, although exhibiting considerable variation 

 in shape and size, appear to be variation of a common form. Most of 

 the specimens are immature. The few mature examples at first glance 

 would naturally be referred to Physa heterostropha Say, but the uniform 

 sculpture of the apical whorls, which becomes more or less obsolete on 

 the body whorl of the mature shell, forbids their reference to that species. 

 The sculpture is that of gyrina and the form may ultimately referred 

 to that species as an extreme form, but the shape of the immature shell, 

 its small, acute spire and deeply impressed suture is quite different 

 from that of typical gyrina. In the present chaotic state of the nomen- 

 clature of the American species of Physa it would seem the better policy 

 to refrain from any attempt at specific identification than to run the 

 risk of adding to an already over-burdened synonymy. 



42. Aplexa. hypnorum (L.). 



Range: "Northern Europe, Asia and America. Northern United 

 States and Canada." (Dall). 

 Michigan: Generally distributed. 

 Isle Royale: Not collected in 1905. See Report Exped. 1904, p. 98. 



43. Planorlis trivolvis Say. 



Eange: "Entire Atlantic Drainage of North America; and the Mis- 

 sissippi Valley and northward." (Dall). 

 Michigan: Generally distributed. 

 Isle Eoyale: III, 5, Sumner Lake, Nos. 78 A, 135. 

 In a small pool in the sedge zone of a tamarack swamp. 



44. PlanorMs Mcarinatus Say. 



Eange: "The United States East of the Rocky Mpuntains; Eastern 

 Canada; Oregon." (Dall). 



Michigan: Generally distributed. 



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

 Bulrush Zone at westeni end of Rock Harbor, Nos. 159, 160; III, 6, 

 Southwest Coves of Rock Harbor, No. 91. 



Dredged from the mud bottom at the upper end of Rock Harbor, near 

 mouth of a small stream, in 3-5 feet of water (Nos. 159, 160). 

 , 44a. var. striatus Baker. 



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

 No. 162; III, 5, Sumner Lake, Nos. 78 A, 79 A. 



Dredged from the mud bottom of the small sluggish stream at the 

 head of Rock Harbor (No. 162) and from the margin and sedge zone 

 of Sumner Lake (No. 78 A, 79 A.). 



