PAPERS ON ZOOLOGY 277 



1913, pp. 179-200). This study was made when pollu- 

 tion "was at its maximum and during the period when 

 mollusean life had disappeared from the lower j^art of 

 the river. The dissolved oxygen in the lower river, be- 

 low the trunk line sewer, in July and August when the 

 temperature was high and the water low, varied from 

 5 to 41 per cent of saturation. The water at the bottom 

 of the river almost always contained less oxygen than 

 that at the surface. On one day in August, the percent- 

 age of saturation in a distance of three miles did not 

 exceed 5 per cent from the surface to the bottom of the 

 stream, which lias a depth of about twenty-six feet. The 

 number of bacteria per cc. for this period was 1,650,000 

 near the source of pollution and but 67,000 near the 

 mouth of the river where the influence of the pure water 

 from Lake Ontario increased the amount of dissolved 

 oxygen. 



In 1917 a large part of the city sewage was diverted 

 to a disposal plant situated near the shore of Lake On- 

 tario. Here an average of 32 million gallons of sewage 

 are treated daily and the treated sewage discharged into 

 Lake Ontario in deep water at some distance from the 

 shore. It is at once apparent that when this large amount 

 of sewage was discharged into the Genesee Elver iii a 

 crude condition, it could not but render the water totally 

 unfit for animal life and a menace even to the inhabitants 

 who visited the beautiful parks bordering both sides of 

 the lower Genesee Eiver. 



The result of the diminution in the amount of sewage 

 discharged into this river has been that the mollusean 

 fauna, as well as other forms of animal life, have re- 

 turned and are rapidly taking possession of the favorable 

 environments which were in use previous to the maxi- 

 mum period of pollution. Collections made in Septem- 

 ber, 1919, contained six species, two being water-breath- 

 ers and four air-breathers : 



Musculium trausversum Planorhis trivolvis 

 Bytliinia tentaculata Pliysa Integra 



Galha catascopium Phi/sa oneida 



