The Marine Fauna Section of the Instituto Paulista de Oceanografia (São Paulo Oceanographie Institute), has undertaken regular plankton researches along the coastal waters of São Paulo State (Brasil), as an index of their productivity. After examining 297 superficial plankton samples from different areas and seasons, the author found a specimen of Ceratium that was considered very close to Ceratium furca Dujardin var. báltica (Fig. 1). whose occurrence called his attention due to the fact of having on its right side a third supplementary appendix longer than that of the characteristic plate of both species Ceratium hirundinella and macroceros. Up to now, isolated individuals were observed with pre or post-cingular plates which exhibit a variable thikness. Frequently, were found somewhat strong deviations on the right or on the left side of the soecimen examined. Regarding the extra appendix considered here to be a specific variation, the author thinks that nothing definite can be said at present since only one such individual was caught. In the other hand he thinks that this specific variation is worthwhile noticing.
