ECOLOGY OF ISLE ROY ALE. 291 



Apparently most frequent in shallow water in places sheltered from 

 the waves, but No. 220, a single very young specimen, was collected on 

 the under surface of a water-lily leaf. 



With one exception, tjie specimens from all these localities are alike 

 and belong to the commion, rather short, lake form of this species. As- 

 sociated with this form at Station IV, 6, was a very thin, elongated 

 form with the chaxacteristic sculptui'e of catascopium, which is closely 

 related to, but much more fragile than, the elongated form, which is 

 characteristic of the lower Great Lakes. 



37. Limnwa sp? 



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

 No. 163 ; iv, 2, Island No. 14 in Tobin Harbor, No. 126. 



At both these localities occurred a few dead, fragmentary and more 

 or less decayed specimens, which could hardly be referred to any of the 

 sjpecies listed above, and yet were too imperfect to successfully identify. 



38. Physa smyii Tapp. 



Eange: Northern United States and Canada. 



Michigan: Generally distributed. 



Isle Royale: I, 1, Lake and Bay Beaches, Nos. 50, 57, 118, 125; 3rd 

 Cove west of Camp on Light-house Peninsula, No. 7; III, 4, Head of 

 Sumner Lake Trail, (Wood); V, 1, Beach at Siskowit Bay, No. 200; 

 Washington Harbor, (Wood). 



The specimens from Washington Harbor are of normal thickness and 

 more nearly typical in shape than those from the. other localities, which 

 are unusually thin. 



More detailed notes on the local distribution of this species are given 

 in the chapter by H. A. Gleason. 



30.* Physa gyrina Say. 



Eange : "The United States east of the Mississippi, Canada and north- 

 ward." (Ball). 



Michigan : Generally distributed. 



Isle Eoyale: II, 5, Forbes Lake, Nos. 71 A, 90; III, 5, Southwest 

 Coves of Rock Harbor, No. 91. 



Specimens No. 71 A were found on driftwood in water a few inches 

 deep. 



The specimens from Forbes Lake are a very large, inflated form. Those 

 from the other locality are much smaller and may be one of the varying 

 forms of No. 41, though closer to typical gyrina than those included 

 under that head. 



40.* Physa aplectoides Sterki. 



Range: "Tuscarawas County, Ohio, and elsewhere." Sterki. 



Michigan: Isle Eoyale. 



Isle Eoyale : V, 11, Tamarack Swamp, No. 128 A. 



Taken from foot-print pools in the Sedge and Buck Bean Zone 

 about a small pond. 



The occurrence of this minute species so far from its original locality 

 in Ohio, was one of the surprises of the 1905 collection. It is a very 

 distinct form resembling a young Aplecca hypnorum in shape but beauti- 

 fully sculptured, especially on the apical whorls. The identification is 

 based on comparison with topotypes of aplectoides received from Dr. V. 

 Sterki. 



