The Relation of Mollusks to Fish in Oneida Lake 133 
lake. The statement made by Petersen, that the bottom con- 
ditions and fauna of the habitats examined by him remained 
practically unchanged for a period of twenty years (op. cit. 
p. 4) is significant and should be borne in mind when making 
quantitative studies in Oneida Lake. 
It is to be especially noted that where a great abundance 
of vegetation exists, choking the water, there will he few if 
any mollusks. Dr. Jean Dawson, after making exhaustive 
studies upon Physa and Lymnea, came to the following con- 
clusions (op. cit. p. 29) concerning this feature: 
1. Where the pond weeds have captured quiet waters, there were found 
no snails alive or dead. 
2. Snails live in moderate numbers where there is a luxuriant growth 
of weeds if there be a considerable depth of water above the 
plants, or if the water is gently flowing over them. 
3. The snails occur in the greater numbers where there is a moderate 
amount of water plants and organic debris. 
Tt is probable that the abundance of molluscan life in 
Oneida Lake, where the submerged vegetation forms a heavy 
mass, is due to the amount of fresh water which is forced 
into the protected bays by the waves. An adequate oxygen 
supply seems to be the important factor, 
C. MOLLUSCAN Foop HABITS. 
The abundance of molluscan life is dependent upon a favor- 
able environment and a sufficient supply of food. The water 
must contain a sufficient supply of oxygen, produced by eur- 
rents of water, bringing in a fresh supply of water or aerating 
the water present by means of air currents which move the 
liquid medium. Plants also furnish some oxygen. There 
must also be a proper substratum or bottom, a requisite depth 
of water, and the plants or animals necessary for food require- 
ments. Oneida Lake contains all of these conditions in 
abundance. 
Mollusks may be divided into consumers or predaceous and 
producers or vegetarians. The former are predatory, feeding 
upon other animals or their own kind, the latter are mostly 
vegetable feeders and convert plant material into mollusean 
