In this paper all the known species of the genus Cuna known from the American Atlantic and South African coasts are revised, creating for Cuna dalli Vanatta a new genus Goniocuna, detached from Cuna on account of its not differentiated prodissoconch, and the absence of lunula and impressed escutcheon. Another new genus, Americuna, with A. besnardi n. sp. from the South Western Atlantic coast, is characterized by its strongly inequilateral outline, very conspicuous strong ring surrounding the prodissoconch, and the very much elevated hinge with both lateral and marginal teeth on the right valve while in the left they are separated from the edge by a groove. Cuna concentrica Bartsch 1915 (pre-occupied by Hedley 1902) should be replaced by C. gemmula Turton 1932, being this the first valid name available.