Fossocytheridea Swain & Brown and
Perissocytheridea Stephenson are genera characteristic of brackish water environments. In 51 samples from the Santonian-Campanian, from the well 9-MO-13-RN, Potiguar Basin, Brazil,
Fossocytheridea potiguarensis Piovesan, Cabral & Colin,
Fossocytheridea POT 1 Piovesan, Cabral & Colin and
Perissocytheridea jandairensis Piovesan, Cabral & Colin have been identified. In the São João das Lampas section (middle Cenomanian), Lusitanian Basin, Portugal, 25 samples were studied and
Fossocytheridea merlensis (Babinot & Colin) and
Perissocytheridea estribeirensis Andreu have been recognized. The distributional pattern of the
Fossocytheridea-
Perissocytheridea assemblage, combined with analysis of the abundance and diversity of marine ostracodes, suggests that in the Late Cretaceous
Fossocytheridea and
Perissocytheridea were euryhaline genera, and that the tolerance to salinity gradients is related to the ecology of each species and not strictly to that of the genus.