Occasional Papers of the Museum of Zoology 1 1 



b€ divided into three quite distinct subzones. The inner of 

 these was characterized by a thin layer of muck, formed of 

 bits of bark, twigs and other organic material, which covered 

 the sand and into which many water-soaked logs have sunk. 

 This reached out into about 12 inches of water, where the 

 mucky bottom became much thinner; here was a narrow zone 

 of a thick, intermeshing growth of aquatic moss. Beyond this 

 moss zone the bottom is of cleaner sand with comparatively 

 little organic material out to the inner plant zone and the thick 

 layer of muck accompanying the latter. 



The larger Planorbes, Physa, Ferrissia parallela, and Planor- 

 bis e.vacuoits were mainly found on the logs, etc., of the inner- 

 most zone; Campeloma decisunt and Sp^ucrinm sulcatum were 

 the burrowing forms of the same region. The different spe- 

 cies of Amnicola and A'alvata were more abundant in the 

 outer two zones. Amnicola was more characteristic of the 

 water-moss zone, and Valvata seemed to prefer the sandy 

 bottom itself. Anodonta marginoita, Splucrium stamineiim and 

 the various species of Pisidium were mostly found in the outer 

 zone, burrowed in the sandy bottom. 



Habitat 6. Mouth of East Branch. In the mouth of the 

 East Branch the conditions of the river grade into those of 

 the lake. In these places the bottom was clear and sandy, and 

 but little current was discernible. Valisneria spiralis was 

 sparsely scattered through the shallow water near the banks. 



A large proportion of the molluscs collected consisted sim- 

 ply of dead, chalky specimens forming a sort of marl deposit 

 in the depressions. These might have come originally from 

 almost any aquatic habitat in the region, although the living 

 species were also found in these deposits in even greater 

 abundance. The species that were only found in these deposits 



