A new genus of limnic ostracode, Sinuocythere n. gen., belonging to the family Limnocytheridae, subfamily Timiriaseviinae, and three new species, Sinuocythere subsinuosa n. sp., Sinuocythere pedrogaensis n. sp. and Sinuocythere candeeirosensis n. sp. are described. This genus belongs to the Timiriasevia-Metacypris group, which first appeared at the end of the Triassic and began to diversify during the Middle Jurassic. It differs from other members of the group by its elongate subovate carapace, slightly compressed posterior margin, and its sinuous and posteriorly upturned dorsal margin. All the known species of this genus have a stratigraphical distribution limited to the Middle and early Upper Jurassic (Bathonian-Oxfordian) of the southern Tethyan realm (Tunisia, Morocco and Portugal). Sinuocythere has a typical euryhaline behavior, contrasting with the salinity tolerance of living and fossil species of the genera Metacypris and Vecticypris, which are essentially limnic-oligohaline.