United States Department of the Interior 
Oscar L. Chapman, Secretary 
Fish and Wildlife Service 
Albert M. Day, Director 
Explanatory Note 
The series, Special Scientific Reports, embodies results 
of investigations, usually of restricted scope, intended to aid 
or direct management or utilization practices and as guides for 
administrative or legislative action. It is issued in limited 
quantities for the official use of Federal, State or cooperating 
agencies and in processed form for economy and to avoid delay 
in publication, 
Washington, D. C. 
November 1950 
