The [elation of Mollusks to Fish in Oneida Lake 287 
are intact and from these the genera may be distinguished. 
To aid in the identification of snails by this means the oper- 
cula of several genera are figured on this page (fig. 48). 
The four genera are: 1, Goniobasis; 2, Bythinia; 3, Amni- 
cola; and i Valvata. 
The number of individuals eaten by a fish may often be 
known by the number of opercula present. 
3. Tasie or DistriBUuTION OF SPECIES. 
In the table at the end of this chapter the 62 species and 
varieties of fresh water mollusks are so arranged as to indi- 
eate their distribution throughout the 54 stations and sub- 
stations. It will be noted that the habitats producing the 
largest number of species are those with a sandy or rocky 
bottom in an exposed situation. Of those habitats, having 
10 or more species, eight are exposed points or shores where 
Fig. 48. Opercula of small gastropods, 1, Goniobasis; 2, Bythinia ; 
3, Amnicola; 4, Valvata, All are enlarged. 
the number of species ranges from 10 to 17. One is a sandy, 
protected bay, with 16 species and another has a sandy shore, 
partly protected, with an abundance of vegetation such as 
Water Willow, Bulrush and Pickerel-weed, and is inhabited 
by 27 species. The variation in the number of species found 
in each habitat is shown on the table and need not be dwelt 
upon farther. 
