A NEW SPECIES OF RETISPIRA KNIGHT (GASTROPODA, BELLEROPHONTOIDEA) FROM THE LOWER PERMIAN OF CHUBUT PROVINCE, ARGENTINA. A new species of Retispira Knight (Gastropoda, Bellerophontoidea) from the lower Permian of the Tepuel-Genoa Basin, Chubut Province, Argentina, is described. The specimens come from the Cisuralian Euphemites chubutensis - Palaeoneilo aff. concentrica Zone. Retispira patagoniensis sp. nov. is a small, subglobose, phaneronphalus bellerophontid characterized by having a broad selenizone with fine lunulae and spiral lirae. Spiral and colabral elements generate a reticulate pattern. The new species developed in both shallow marine and deltaic facies and its distribution was mainly affected by water turbidity, depth and temperature. Its feeding habit may have been herbivorous, probably as an algal foliage dweller.