During 1941 the E. W. SCRIPPS made ten cruises off southern California, each covering the same area of about 80,000 square kilometers. The cruise plan consisted of a grid of approximately 40 stations. At each station a catch was made with the Allen five-liter closing bottle every ten meters from the surface to 60 meters. The catch was filtered through a net of No. 25 silk bolting cloth, and the diatoms so collected were later identified, counted and recorded as the number of diatoms per liter....