The Productivity of fish Food in Oneida Lake 99 



species of mollusks out of 33 make up 7O.07 per cent (1,796 

 individuals) of the total number. These are Sphccrium ver- 

 monlannni (458), .Imnicola (four species, 941 individuals), 

 Galha ca!ascopiu)n (133 individuals), and Planorbis parvus 

 (154 individuals). Two species of Amnicola make up the 

 greater part of the number of that genus (947 individuals). 

 The Galha are all young, and probably do not live in this habi- 

 tat when adult, seeking the rocky and gravelly shores when 

 approaching maturity. 



As Petersen has pointed out ('13, pp. 4-5) some of the ani- 

 mals occurring in c|uantitative collections are seasonal, being 

 present in abundance at one time and wholly or partially want- 

 ing at another time. Galba and Fhysa are examples of this 

 seasonal occurrence of species, living in the algae of the bottom 

 when young and immature and seeking the rocky or gravelly 

 shores when approaching maturity. Therefore, the character- 

 istic species of mollusks on the sand bottom are Sphccrium 

 vermontanum, Amnicola oneida, bakeriana, and hakcriana 

 nimia, and Planorbis parvus, five species. It should perhaps 

 be called a Sphcrrium-.lmnicola community. Though not 

 found in any number, the gastropod Campeloma is very char- 

 acteristic of the sand bottom, not occurring elsewhere except 

 on a clay bottom in several habitats. The large number of 

 Pisidium, 1 1 species, is noteworthy. 



When the associated animals are considered a few striking 

 features are apparent in the table. Oligochate worms make 

 up 28.55 P^^' c^"^ "^ the total number ('/2^) and chironomid 

 larvae 41.55 per cent (1,052). The large number of amphi- 

 ]iods, of which Hyalella is the most abundant, and the number 

 of species (7) and individuals (138) of Cladocera is note- 

 worthy. Many of these animals are seasonal and would nor 

 occur in such numbers at other times of the year. Such are the 

 dipterous and trichopterous larvae, and certain other insect 

 larvae and nymphs. Earlies in the year the May-fly nymphs 

 are probably of much greater abundance, judging by the heavy 

 flights of adult May-flies observed in June. At the time of 

 year in which the present studies were made (July) the oligo- 

 chiete worms and chironomid larvae are the characteristic 

 species of associated animals as regards numbers. The im- 



