The Spheniopsidae Gardner, 1928 comprises four living species of Spheniopsis Sandberger, 1861 and eight of Grippina Dall, 1912, the latter restricted to the Pacific Ocean, the former also occurring in the Atlantic. Spheniopsis brasiliensis new species and Grippina coronata new species are described from the Brazilian southeastern coast, based on a detailed study of their shells. They are distinguished from already described species mainly by differences in the outline of the valves, external sculpture and right hinge dentition. Shallow micro-pits present all over the outer surface of the dissoconch are viewed as similar to those already described for cuspidariids. They may, thus, represent further evidence for the relatedness of spheniopsids and cuspidarioideans. The new species from Brazil represent the first finding of these rare minute bivalves of this family from the southwestern Atlantic.