154 THE ROYAL SOCIETY OF CANADA 



1. Marshy bottom - 1' 



2. Soft mud bottom depth . 1' - 6' 



3. Rock debris " " ....'.... 1' - 4' 



4. Blackish brown mud bottom 10' - 20' 



5. Red ooze " " 20' - 32' 



6. Sandy " " 0' - 6' 



7. Marly " " 0' - 6' 



In zone 1 where the plant life floating and almost submerged fills 

 the whole of the water, there is to be found Lymnaea stagnalis appressa 

 floating on top in considerable numbers. It is a thin large shelled 

 form^which cannot stand exposure, and is found only in well protected 

 places. Here also is to be found Pseudosuccinea columella and Ancylus 

 rivularis. Occasional Valvata is to be found also. The small number 

 of species and individuals in such a habitat seems to follow the general 

 rule that where plants have captured too much of a great water area, 

 molluscs are rare. Where plants are quite abundant but the water is 

 in motion, a considerable number of molluscs may be present. Where 

 the plants are moderate in number and the bottom covered with some 

 organic debris the molluscs are at their best. 



Zone 2 furnished the greatest number of specimens and species 

 of any habitat in the lake. Here were found every species listed with 

 the exception of Campeloma decisum, Lymnaea stagnalis appressa, and 

 Pseudosuccinea columella. Here there is a moderate amount of vege- 

 tation, few algae, but many fresh pond lilies. The smaller forms were 

 attached to the stems in many cases while Planorbis campanulatus 

 and Physa heterostropha were attached either to the upper or lower 

 sides of the pads. Planorbis parvus was also frequently found on the 

 leaves. P. exacuous and P. antrosus were brought up mostly in 

 dredging from the bottom. P. trivolvis was usually attached to 

 submerged or floating logs. The pond lilies and allied plants serve 

 as support, shelter, and food for the above forms. Physa especially 

 was seen feeding upon the leaves. The larger bivalves such as 

 Lampsilis radiata and Anodonta fragilis were observed in this habitat 

 but near the outlet where there was a perceptible current. On the 

 mud and debris at the bottom Valvata tricarinata, Amnicola porata, 

 and the small forms of Pisidium and Sphaerium occur in great abund- 

 ance, all showing the natural shade of their epidermis. 



Zone 3 is a specialized habitat on the west side of the lake at the 

 foot of the rock clifïs already mentioned. Here every spring a consid- 

 erable amount of clay and rock debris are washed into the water, 

 forming a sort of miniature delta. During the summer some of the 



