152 Collcyc of Forestry 



assume a Hg'lit greenish color similar to that of the alga?. The 

 relation of the algae to the mollusks is shown in Tables No. 16 



to35- 



The abundance of alg^e was probably the cause of the com- 

 parative absence of mollusks from the larger plants — Myrio- 

 phyllum, Potatnogeton, Elodea, etc. — the algse forming better 

 foraging ground than the higher plants. The absence from 

 the higher plants may also have been partly due to season, for 

 in September of the previous year mollusks were noted in 

 great abundance in the submerged vegetation of the outlet of 

 the lake near Brewerton (Baker, '16, p. 129). 



2. Relation to the Bottom. Mollusks usually clearly 

 reflect the physical character of the environment, certain 

 species being characteristic of a given habitat, preferring this 

 to any other and being dominant in point of numbers. In 

 Lower South Bay six types of bottom occur, boulder, gravel, 

 sand, sandy clay, clay, and mud. In this bay, however, the 

 effect of the different kinds of bottom is greatly modified by 

 a mass of filamentous algae which covers large areas of the 

 bottom like a blanket and makes a uniform algal habitat over 

 diverse kinds of bottom. That the character of the under- 

 lying stratum does play some part in the ecological distribu- 

 tion of mollusks in the bay is shown by the diagram (Table 

 No. 43) where all of the species inhabiting the bay and the 

 immediate vicinity are listed in relation to this distribution. 

 It will be noted that 12 species live on six kinds of bottom, 

 10 on five kinds, 7 each on three and four kinds, 8 on two 

 kinds, and 21 on one variety. These figures show that there 

 is a selection of habitat based on the nature of the bottom 

 material. The table also shows that 50 species live on a mud 

 bottom, 42 on sand, 35 on clay, 33 on gravel, 27 on boulder, 

 and 25 on a sandy clay bottom. 



The table brings out clearly the distribution according to 

 character of bottom and extended discussion would be super- 

 fluous. It may be well, however, to point out those species 

 which may be said to be characteristic of each variety of 

 bottom. In the boulder habitats Goniobasis livescens, Lymncra 

 stagnalis lilliancc, Galha catascopium, Planorhis hinncyi and 



