In this paper, 54 species of Diatomaceae are studied belonging to 8 genus of the group Naviculoideae, from samples collected at 6 different points of the Brazilian coast, between 17º - 25º lat. S, approximately. One genus and 30 species are recorded for the first time in Brazilian waters and a new variety densestriata is proposed for Pleurosigma elongatum W. Sm. The material examined comprised plankton, bottom samples, and seaweeds from which the Diatoms were taken by suitable methods. The genus and species are listed in alphabetic order.