The fossil turtle Tropidemys langii is a representative of Plesiochelyidae, a traditionally recognized group of Late Jurassic turtles diagnosed by the presence of three cervical scutes and adapted to life in the sea. Tropidemys langii was previously only known from fossilized carapaces and, possibly, plastra from Europe, most notably the famous ‘Solothurn Turtle Limestone’ of Switzerland. Due to the sparse fossil record of Tropidemys langii, several questions concerning its taxonomy and phylogeny have remained unanswered. Here, new material of Tropidemys langii is reported from the Kimmeridgian of Porrentruy, Canton Jura, Switzerland. In addition to three well-preserved carapaces, associated plastra and limb bones (humerus and femur) are described for the first time. The type specimens of ‘Tropidemys valanginiensis’ and ‘Pelobatochelys blakii’ lack diagnostic characters, but can nevertheless be referred to Tropidemys. A potential extension of the lineage into the Early Cretaceous is uncertain, however, because the type locality of ‘Tropidemys valanginiensis’ is dubious. A cladistic analysis shows that Tropidemys langii is sister to Plesiochelys solodurensis, thereby tentatively confirming for the first time the monophyly of Plesiochelyidae using cladistic arguments.