Transmission electron microscopic examination ofCephaleuros virescensKunze growing on leaves ofCamelliasp. indicates that gametes are similar to those ofTrentepohlia aurea. The gametes bear two, smooth isokont “keeled” flagella containing typical “9 + 2” axonemes and lacking scales. Flagellar insertion is apical and the parallel basal bodies overlap laterally. Each basal body is associated with a separate multilayered structure and component microtubular spline. The latter extends posteriorly beneath the plasmalemma. A nucleus, mitochondria, chloroplasts, and cytoplasmic haematochrome droplets are present. Pyrenoids and eyespots are absent. The subcellular components ofC. virescensgametes are comparable to those found in gametes ofT. aurea; however, the arrangement of basal bodies and multilayered structures differs slightly from that inT. aurea. Comparison of the fine structure of gametes fromCephaleuros, Phycopeltis, andTrentepohliaclearly indicates that the (1) mode of flagellar insertion, (2) morphology, number, and arrangement of multilayered structures, and (3) keeled flagella are common to these three genera and, thus far, unique among the green algae. Although flagellar insertion is apical, it is not bilaterally symmetrical (sensu stricto), nor is it asymmetrical (cf.CharaandNitellasperms). The arrangement may be termed “reversed bilateral symmetry” and standardization of the terminology is recommended.