SYNOPSISThe species of the genusMallomonas, classed amongst the algæ, are small cells covered with characteristic silica scales and bristles. These are of considerable importance in the classification of the species, but only the coarser details are visible under the optical microscope. A direct electron microscope study yields much information about the fine markings on the scales, but the use of carbon replicas produces clearer, more easily interpreted micrographs, and permits the examination of the exterior of a complete organism.The scales and bristles of nine species, three of which are new, are described, and some variations in the markings within a single species are illustrated