ECOLOGY OF ISLE ROYALE. 289 



Michigan: Generally distributed. 



Isle Royale: Only a single specimen was collected, the exact locality 

 of which was lost, 



30. CarycMwn exile cmiadense Clapp. 

 Range: Northern United States and Canada. 



Michigan: Generally distributed north of the Saginaw-Grand Valley. 

 Isle Eoyale: Not collected in 1905. See Report Exped. 1904, p. 97., 

 where it is listed as Garychium exile. 



31. Lymncea stagnalis (L.). Fig. 63. 



Range: "Europe; the Caucasus; Western and Northern Asia; the 

 Northern United States; Canada and British America." (Dall). 



Michigan: Generally distributed. 



Isle Royale: 



Variety A. (Fig. 63, No. 1.) II, 1, Mouth of Benson Brook, No. 167; II 

 4, McCargoe Cove, No. 53 ; III, 2, Small Island in Rock Harbor, No. 89 

 III, 3, Bulrush Zone, Head of Rock Harbor, Nos. 161, 162, 168; III, 4, 

 Sumner Lake Trail, on Rock Harbor, No. 156; III, 5, Sumner Lake, No 

 155; III, 6, Southwest Coves of Rock Harbor, Nos. 91, 95; North side of 

 Rock Harbor, No. 110; IV, 6, Small Island in Tobin Harbor, No. 123 

 ^Vashington Harbor (Wood). 



Variety B. (Fig. 63, No. 3.) I, 1, Lake and Bay Beaches, Nos. 32, 50, 57 

 3rd Cove below Camp on Light-house Peninsula, No. 7; II, 1, Mouth of 

 Benson Brook, No. 54; III, 4, Head of Sumner Lake Trail, (Wood) ; V, 

 1, Beach at Siskowit Bay, No. 200. 



Variety C. (Fig. 63, No. 6.) V, 6, South shore of Siskowit Lake, Nos. 

 199, 210, 211, 217. 



Notes on the habitats of this species are given in detail in the chapter 

 by H. A. Gleason. 



This large and widespread species seems in this country at least, to 

 exhibit its greatest variability in the Lake Superior Region. Two well 

 marked varieties have already been described; one var. higleyi Baker 

 from Michipicoten Island on the north shore, and the other var. sanctrp- 

 maricB Walker from the St. Mary's River. It is apparently one of the 

 most abundant species on Isle Royale, where three very distinct for-.>is 

 are represented, none of which are typical and none exactly coincident 

 with any of the described varieties. All the specimens collected fall 

 into one of these groups which are apparently correlated with definite 

 local conditions. For present purposes they may be designated as 

 varieties A. B. and C. Variety A (Fig. 63, No. 1) most closely approaches 

 to the usual North American form known as var. appressa Say (Fig. 63, 

 No. 4) from which it diflCers mainly in the pear-shaped rather than regu- 

 larly rounded aperture. It is characteristic of the quieter waters of the 

 long, narrow harbors which are such a remarkable feature of the island. 

 The same form has also been collected in the St. Mary's River near the 

 Neebish Rapids. Variety B is an inhabitant of the shores exposed to the 

 more violent waves of the main lake. Correlated with these conditions 

 the shell is smaller, with a short spire and a relatively large body whorl 

 for the accommodation of the large foot necessary to enable it to re- 

 tain its hold upon the rocks, among which it lives. This form (Fig. 63, 

 No. 3) is more nearly related to the var. higleyi (Fig. 63, No. 5) from the 

 north shore, but is apparently much smaller. It is about the size of the 

 38 



