The results of two analytical procedures, viz., percent cubicity by dye adsorption and supersphere roundness index, Q , by electron image analysis (electron microscopy) were compared for a series of cubic AgBr emulsions. A linear, least square, correlation, % cubicity = -110.7 Q + 99.96, was obtained in the range 0.25 < Q < 0.65. The zwitterionic dye, 3-ethyl, 3'-(3-sulfo-butyl)-9- methyl-thiacarbocyanine, as used in the cubicity test, adsorbs on rounded AgBr cubes either as single molecules or as J-aggregates.When cubes are slightly or moderately rounded, the demarcation of these two modes of adsorption can be identified with a “tilt” of the grain surface between 9° and 13°: only small deviations from the {100} crystal habit suffice to cause the dye to adsorb as J-aggregates.