Net phytoplankton samples (30 f.lm and 54 f.lm mesh), from coasts of the Pacifíc Ocean of Mexico, including coasts of Baja California, the Gulf of California and Tehuantepec (1982-1986), were analyzed to provide a revision of specíes of the diatom genus Coscinodiscus. Síx specíes were found and studied by light and electron microscopy. Typical references, morphological details, and a brief discussion on morpho10gical variability and taxonomic aspects are given for each specíes, as well as the local and general distribution. Coscinodiscus radia tus appeared as the most widespread species, perhaps because sorne taxa have become minor synonyms of it. T he valuable taxonomic characteristics of the genus Coscinodiscus are: form of the val ve, presence of valve process, relative height of mande, other specific characteristics
Keywords: phytoplankton, diatoms, coscinodiscus, morphology, taxonomy, distríbution, mexican pacifico