The author describes two new species: Protoperidinium steidingerae and Gonyaulax Rutnerae, and a third, little known species, Protoperidinium norpacenses. Balech. The three of them were collected in plankton tows in the South Brazilian littoral. The present study of P. norpacense completes the original description and shows some differences with the thecae from the tropical Pacific. Its relationships with P. heteracamtum Dangeard are discussed. P. steidingerae has been described, by Steidinger & Williams as P. oblongum. It is close to P. venustum but it has several very peculiar features: pointed anterior horn; first apical plate conspicuously shorter than the epitheca; neither 1' nor 3' reach the apex where 2' is largely connected with 41 on the ventral side; seemingly there are no platelets P and X, Gonyaulax kutnerae, belongs to the tamarensis group: its size, shape and weak thecawalls and tabular details tell it apart from the other species of the group. The only species which is somewhat alike is G. brvisulcatum Dangeard which is almost a nomm nudum. Recently Taylor (1976) described as G. brevisulcatum a species which clearly differs from G. kutnerae and which seems to be a Peridinella.