162 MOLLUSCA. 



Walker were obtained on leaves on the bottom of a large swamp (19) 

 on Sand Point, on driftwood along a marshy shore in the upper por- 

 tion of Pigeon River (23) and in a sand pool on the beach at Little 

 Oak Point (6). They are small and narrow. An example from Sand 

 Point measures: altitude 6.5mm., width 3mm., aperture length 3mm., 

 aperture width 1.5mm. 



Lymnaea obrussa, var. approaching decampi (Streng). — A juvenile, 

 very fragile shell found at Raymond's Point (14) and heavier, adult 

 specimens obtained from off Dune Point (15) are intermediate be- 

 tween the typical species and the variety. 



52. Lymnaea obrussa, var. decampi (Streng). — Typical specimens 

 of this form were obtained from the shallow water off Dune Point 

 (15). An example measures: altitude 9.25mm., width 4.75mm., 

 aperture length 4.5mm., aperture width 2.75mm. 



53. Lymnaea humilis Say. — A single specimen of this shell was 

 found on floating driftwood in the mucky part of Turtle Bay (8). A 

 few specimens were also obtained from driftwood in the ox-bow pond 

 near the mouth of Pigeon River (22) and along a marshy bank of the 

 river itself (23). A considerable number of shells were .collected in 

 rocky pools along the north shore of Stony Island (3). 



54. Lymnaea catascopium Say.^ — A single dead shell of this species 

 was found on the north shore of Sand Point. It had probably been 

 washed up from deep water (1) as that is the only habitat in the 

 neighborhood that it could have come from. The shell is quite large, 

 measuring: altitude 21mm., width 12mm., aperture length 12.5mm., 

 aperture width 7.5mm. 



55. Lymnaea emarginata, var. ontarioensis (Miihlfeldt). — This 

 form was very abundant on hmestone rock off the north shore of 

 Stony Island, on the docks in the same locality (2) and in the rock 

 pools along the shore (3). The shells are quite heavy,, and are almost 

 pure white outside and pinkish inside. There is considerable variation 

 in size among them. Some are malleate, others not; some are long 

 and narrow with the aperture only about one-half as long as the en- 

 tire shell, others are wdde with the aperture almost two-thirds the 

 length of the shell. Extremes measure: altitude 18.5mm., width 

 9.75mm., aperture length 10mm., aperture width 9.75mm.; and alti- 

 tude 15.5mm., width 11mm., aperture length 10.25mm., aperture 

 width 7.5mm. Some of the shells are perforate but the majority are 

 not. 



56. Lymnaea palustris (Miiller). — In this region, Lymnaea palu- 

 stris was the characteristic shell of the temporary swamp (18). Ow- 

 ing to the work being done in the summer, a large part of the shells 

 were found buried in the leaves, aestivating, where ponds had been 



