178 



able for Anodonta life, except for the preseuce of the muskrat. Ano- 

 dontas are absolutely absent from water some distance from his home, 

 where we found Unios rather abundantly. This points to the fact 

 that the muskrat confines the Anodonta to the deeper waters at the 

 edge of the sandy and gravelly banks. 



It seems to us that the foregoing facts give basis for the following 

 conclusions: First, that the mussel zone lies mainly upon sandy and 

 gravelly banks, and on the outer edge of the same; second, that wave 

 action and the muskrat determine the limit of the distribution shoreward, 

 and that tlie character of the bottom is the pi-mcipal factor determining 

 the outer boundary of the zone. 



(JlXI.edcntula. 

 + = U. lubiQiuoSus. 



JamesSirrvoKTow 

 T J. Htadlee. 



