Despite variations in pore diameter and pore concentration between 22 species of planktonic Foraminifera, shell porosites are relatively uniform for those co-occurring in the same latitudinal belts: over 10 percent for tropicalsubtropical species; 5 to 10 percent for temperate species; and less than 5 percent for subpolar-polar species. Shell porosities of fossil planktonic Foraminifera may be useful indices for interpreting Cenozoic climates.