156 THE AMEBIC AN NATURALIST [Vol. LIV 



viduals. An examination made in 1910 failed to discover 

 a single living mollusk of any species. Apparently, the 

 water had reached such a state of concentrated pollution 

 that even the air-breathing mollusks, which normally 

 come to the surface to take in free air, could not adapt 

 themselves to this unfavorable environment and were 

 either killed or compelled to migrate down the river to a 

 point where the pollution was not so great, a distance 

 of several miles. During the following two or three 

 years the river was visited but no mollusks could be 

 found. 



On March 17, 1917, a large part of the city's sewage 

 was diverted to the Irondequoit sewage disposal plant 

 located on the shore of Lake Ontario near the Durand- 

 Eastman Park. Here an average of 32 million gallons 

 of sewage are treated daily, and the treated sewage dis- 

 charged into Lake Ontario at a distance of 7,000 feet 

 from shore in water 50 deep (vide city engineer's state- 

 ment). It may easily be seen that when this large amount 

 of sewage, untreated, was discharged into the Genesee 

 River, it could not but render the water totally unfit for 

 animal life and a menace even to the inhabitants who vis- 

 ited the beautiful parks bordering both sides of the river. 



The result of the diminution of the amount of sewage 

 discharged into the river has been that the fauna has re- 

 turned and has rapidly taken possession of the favorable 

 environments which were in use previous to the maximum 

 period of pollution. Collections made in September, 

 1919, contained the six species noted below : 



Musculium transversum Bythinia tentaculata 

 Planorbis trivolvis Galba catascopium 



Physa Integra 



Physa oneida (previously reported as heterostropha) 

 It will be noted that practically the same species re- 

 turned to the Maple wood Park section of the river that 

 lived here before the polluted water exterminated the 

 fauna, indicating, probably, that they migrated up the 

 river from the less affected water below. 



