ECOLOGY OF ISLE ROYALS. 283 



in the Upper Peninsula. The occurrence of Polygyra albolabris (which 

 was not found in 1904) in abundance causes a feeling of surprise that 

 Polygra fraterna [monodon auct.) was not found. In Michigan, its 

 range is coincident with that of alholabris and, according to Dall, it is 

 found as far north as James Bay, Hudson Bay. 



All the specimens collected of Pyramidula cronkhitei were of the 

 anthonyi form as in 1904. 



Among the fluviatile species, however, several forms either pre- 

 viously undiscovered or new to the fauna of the state were found and 

 some interesting facts in regard to their distribution were developed. 

 The division of Lymncea, stagnaUs into thi-ee very distinct forms coin- 

 cident with the character of their habitat is very striking and specially 

 noteworthy. 



The fact that all the larger species of Lymnceidae from Siskowit 

 Lake: Lymnwa stagnaUs, Planorbis dicarinatus and Planorbis cam- 

 panulatus, are well marked varieties peculiar to that lake, is very 

 significant and points to some specially favorable environmental condi- 

 tions, which apparently are not present to affect the fades of these 

 species on other parts of the island. "What these are, if not already de- 

 termined, would be an interesting subject for future investigation. 



The acquisition of the additional material, which has enabled the 

 specific distinctness of Lymnwa pilsiryana to be determined, is a matter 

 of congratulation. 

 . The occurrence of the beautiful little P7i/ysa aplectoides adds a new 

 species to the fauna of the state and affords another instance of ap- 

 parently anomalous distribution, which so frequently puzzles the 

 student. Originally described from Ohio, it has hitherto escaped at- 

 tention in southern Michigan, and its discovery on Isle Eoyale was 

 wholly unexpected. The remarkable form of PlanorMs Mcarinatus 

 from Siskowit Lake was one of the most interesting novelties discovered 

 by the expedition and is a noteworthy addition to the fauna of the 

 state. 



"All the Pisidia, except Pisidiuni idahoense and Pisidium sargenti, 

 are represented by small, and, as it seems, characteristically northern 

 forms, slight and generally of light or pale color. Some are not very 

 characteristic and apparently little different from each other and 

 were rather difficult to work up." (Sterki.) 



The writer again acknowledges his indebtedness to Dr. V. Sterki for 

 the identification of the Sphceria and Pisidia and to Dr. H. A. Pilsbry 

 for the determination of the slugs. Dr. H. A. Gleason, who collected 

 most of the specimens, and Mr. Chas. C. Adams have kindly interpolated 

 the details as regards the local habitats and distribution of the 

 different species. The field numbers by Mr. C. G. Adams are indicated 

 by the letter A; all others are Dr. Gleason's, except a few lots collected 

 by Mr. N. A. Wood. 



Detroit, April 1, 1909. 



3. Annotated List. 



1* Polygyrw aTbolairis (Say). 



Range: "Eastern United States, from Georgia and Arkansas to the 

 Saskatchewan." (Dall). 



Michigan: Generally distributed. 



