The use of photometers or water clarity meters for certain types 

 of plankton determinations has been suggested but undoubtedly will 

 require further development. 



E. SELECTED REFERENCES 



IX- 1. HARDY, A. C. The open sea. Vol. I. Boston: Houghton Mifflin 

 Co. p. 67-83. 1956. 



IX- 2. U. S. HYDROGRAPHIC OFFICE. Instruction manual for oceano- 

 graphic observations. Hydrographic Office Pub. No. 607. 2nd ed. 

 Washington. 210 p. 1955. 



IX- 6 



