PAPERS OX ZOOLOGY 131 



to ini<^Tate down stream if the water way is open. How- 

 ever, no sliells with the dead animals were found in our 

 investigations and it may be that the empty shells and 

 valves found represent beds that have been killed by the 

 sewage in earlier years. It is possible for mussel shells to 

 be preserved for hundreds of years, if buried in the mud or 

 sand, and to retain the epidermis as fresh as recently liv- 

 ing shells, and it is not at all impossible that these empty 

 valves may represent a fauna killed several years ago by 

 the concentration of sewage and wastes. 



Detailed studies covering these and other points are now 

 in progress and additional field work will be carried on in 

 the fall, after which a more extensive paper vrHl be pre- 

 pared. 



