130 ILLINOIS ACADEMY OF SCIENCE 



gave the next highest number of species, 20. More ex- 

 tended, search, however, may increase the number in the 

 Middle Fork. 



During the investigation it was observed that the sewage 

 and wastes which enter the Salt Fork at Urbana, pro- 

 duced a marked effect upon the mussel fauna. In the ditch 

 and Salt Fork above Urbana (Ciystal Lake) four species 

 have been identilied; between Urbana and the first bridge 

 south of St. Joseph, a distance of 14 miles by the stream, 

 only a broken valve of Anodonta grandis and a single valve 

 of Quadriila inidulata were found. It is fair to state, how- 

 ever, that this portion of the stream has not been as thor- 

 oughly searched as that part below St. Joseph, and addi- 

 tional work may change this statement to some extent. Our 

 observations lead us to believe, however, that no molluscan 

 life of the Unionidae character will be found in this part 

 of Salt Fork. Not until a point two miles below St. 

 Joseph is reached do we find a single living mussel, A>20(Zo?i- 

 toidcs ferussacianus. About a mile below the latter sta- 

 tion the mussels become fairly abundant. In the neigh- 

 borhood of Sidne}", 20 miles by stream from Urbana, the 

 mussel fauna assumes good proportions both in number of 

 species and in individuals, a dozen species being recorded. 



The most significant observation made was the sudden 

 break in the fauna about a mile above St. Joseph, Spoon 

 River, which is a large branch joining Salt Fork about a 

 mile above St. Joseph, has a mussel fauna of 12 species 

 about a mile upstream from the junction with the Salt 

 Fork. These gradually decrease as we go down the 

 Spoon River and cease altogether at or near the mouth. 

 One must pass down the stream (the Salt Fork) for the 

 distance of six miles before encountering a mussel fauna 

 of comparable extent. These facts offer adequate evidence 

 that the sewage and wastes affect the environment render- 

 ing it unsuited to the life of these mussels. The struggle 

 for survival is seen in the large number of empty valves no 

 living representatives of which could be found after care- 

 ful search. It is possible that the water is diluted enough 

 in the spring and winter to permit the mussels to migrate 

 up stream for a considerable distance; but the concen- 

 trated condition of the sewage during low periods possibly 

 kills those that venture up stream or perhaps causes them 



