The Producliviiy of Fish Food in Oneida Lake 153 



Physa warrcniana, all adult or nearly so, are the dominant 

 moUusks, and associated with these are the spiral caddis-fly 

 larva Helicopsyche, the beetle larva Psephenus lecontii, and 

 the May-fly nymph Hepiacjenia. In the sand between the 

 boulders Anodonta implicata is characteristic. The gravel 

 bottoms have the same species with the addition of a few 

 species which are characteristic of a sand bottom. On a sand 

 or clay bottom Campeloma decisum, Muscidiiun transversum, 

 and several of the Pisidia are dominant. On the mud bottom, 

 which is richest in number of species, a few moUusks are 

 characteristic, such as Sphceriitm solidtdum, S. sulcatum, sev- 

 eral Pisidiurn, Amnicola emarginata, J'ah'ota sincera, and 

 Segmentina annigera. 



Another notable habitat should here be mentioned, that of 

 the lily-pads. These cover a not inconsiderable area and afford 

 food and lodgment for such molluscan species, as Pseudo- 

 succinea cohiniella and variety chalyhea, Physa warreniana, 

 Ancylus parallehis, and Planorhis parvus. Pseudosucciuca 

 columella and its variety may be said to be quite characteristic 

 of this habitat. 



3. Relation of MoUusks to Depth of Water. From a 

 study of Table No. 44, on w^hich all of the species are plotted, 

 it is seen that the number and kind of mollusk vary with the 

 depth of water, shallow water containing the greater number 

 of species and deeper water the less, the decrease in number 

 being regular and gradual. Dividing the depths into seven 

 parts we find a regular decrease as shown below : 



Table No. 45. Showing Decrease of Mollusks with Depth 



Shore to 6 inches 6 species 



I to 3 feet 46 " 



3 to 6 feet 40 " 



6 to 9 feet 39 " 



9 to 12 feet 29 " 



12 to 15 feet 26 " 



15 to 18 feet II " 



Twelve species appear to be confined to water four feet or 

 less in depth; Anodonta implicata, Lampsilis radiata, Mus- 

 culium triincatiim, M. transversum, three Pisidium, Lymncea 



