The study of the brazilian Atherinidae has not yet been developed. Besides Jordan & Hubb's work (1919, p. 187) and Schultz's revision, very little can be found on the matter. This explains the author's preocupation of examining sistematically the shoals he was given. As a result, a specimen of a genus not yet recorded for brazilian waters has been found in Cananéia, South coast of São Paulo State (Brazil), which has been properly named as Adenops by Schultz. The comparative study of this specimen in relation to those from Colombia and Venezuela, as well as the geographic isolation of the species have given the author the conviction of it being a new species not yet described to which he suggests the name of Adenops dissimilis n. sp. Table 1 presents the comparison of the supposed new species with A. analis and A. argenteus; it has been verified that there were divergencies not only on most of the biometric data but there were also divergents characteristics among the three species. Quick comments are made on the ecology; stomach content has been examined as well as the ecto and endo parasites the results compared with those of the Xenomelaniris brasiliensis (Quoy & Gaim.).
