140 College of Forestry 
41. On dead leaves of Bur-reed (Sparganvum eury- 
carpum). 
Ancylus parallelus, common. 
12. Species on dead Water Celery (Vallisneria spiralis). 
Planorbis campanulatus, common. Physa ancillaria warreniana, com- 
Planorbis hirsutus, rare. mon. 
Galba catascopium, common. 
Fig. 39. Diagram illustrating relation of certain mollusks to vegeta- 
tion. 
1. Acella haldemani on Scirpus smithu. 
2. Planorbis trivolvis, var. (1) and Galba catascopium; (2) 
on Scirpus americanus. 
3. Bythinia tentaculata on Elodea canadensis. 
