Occasion arose recently when the writer required to make a number of comparative areal measurements of irregularly shaped portions of fossil corals in thin section, and it was found that the micrometric methods available were very tedious and involved considerable strain. A micro-planinmter has now been designed by means of which fairly accurate determinations of areas can be made with a minimum of eye strain. Though intended primarily for use with the petrographical microscope with the rotating stage, it can be adapted for use on microscopes of the fixed stage type.