The Productivity of Fish Food in Oneida Lake 105 



On the typical clay bottom the mollusks comprise but 31 

 per cent of the total life present, a smaller percentage than for 

 any bottom habitat except that of boulder. Among the mol- 

 lusks, Amnicola is again the characteristic group of species, 

 Aninicola oncida providing 37.8 per cent of the total animal 

 life. Eight species of Pisidium total 16.8 per cent. Campeloma 

 is a mollusk characteristic of a clay or sand bottom, but does 

 not occur in large numbers of individuals. Among the asso- 

 ciated animals several groups include large percentages ; Oligo- 

 chicte worms 17, amphipods 20, isopods 30.8, and dipterous 

 larvse 15.1. The crustaceans total 54.1 per cent, a somewhat 

 larger ratio than that of the sandy clay habitat (43.3 per cent). 

 The filamentous algae Qidogoniuni, Cladophora, and Spirogyra 

 are a factor here as on the sandy clay bottom. The character- 

 istic animals of the clay bottom are Amnicola, Hyalella, and 

 Asellns. 



Life on the Mud Bottom. The mud bottoms may be 

 divided into three divisions, i, within the 6-foot contour; 2, 

 between the 6-foot and 12- foot contours; and 3, between the 

 12-foot and 18-foot contours. 



I. Shore to 6-foot Contour. Twenty-seven unit areas (Table 

 No. 21) were examined from the shallow water mud bottom 

 area, a total of 525 mollusks and 465 associated animals being 

 collected, or an average of 19.44 mollusks and 17.22 associated 

 animals per unit area and a total animal population of 36.66 

 individuals per unit area. This average shozvs that the mud 

 bottom in shallozv zvater is the richest in animal life, quantita- 

 tively, the sand bottom being second in richness (average 34.21 

 individuals per unit area). Amnicola oneida and Planorbis 

 parvus combined form 51 per cent (31.2 and 19.8 respectively) 

 of the total amount of animal life, while the three species of 

 Amnicola and the same of Planorbis total 69.1 per cent of the 

 individuals represented by the 26 species of mollusks. Of the 

 associated animals, the isopods form 12.4 per cent and the 

 amphipods 28.3 per cent. The group Crustacea comprises 

 49.2 per cent of the associated animals. Dipterous larvae here 

 make up but 17.8 per cent of the total. Amnicola oneida, 



