ABSTRACT. A new eucryptodiran turtle, Xinjiangchelys qiguensis sp. nov. from the Upper Jurassic (Oxfordian ± ?Kimmeridgian) Qigu Formation of the southern Junggar Basin (north-west China) is described. The type material consists of a partial skeleton, including the complete carapace, plastron, nearly all cervical vertebrae, both scapulae, the pelvis and one ulna. It is clearly identi®able as a basal eucryptodire since it lacks the mesoplastron. It is distinguished from other species of Xinjiangchelys by several autapomorphies of the carapace and plastron, such as the ®rst and ®fth vertebrals extending on the peripherals, the plastron with three pairs of gulars, and an intergular which does not contact the hyoplastron. In the postcranium, the scapula with a long acromial and a small scapular process, the pelvis with a short ilial shaft and the elongated cervical vertebrae are characteristic. A new phylogenetic analysis of the in-group phylogeny of the Xinjiangchelyidae is proposed and discussed, resulting in a new classi®cation of the family. Xinjiangchelys (Toxocheloides) narynensis is regarded as a nomen dubium. Shartegemys is referred to Xinjiangchelys, whereas the holotypes of`Plesiochelys' chungkingensis and`P'. latimarginalis are excluded from the genus Xinjiangchelys but included in the Xinjiangchelyidae.KEY WORDS: Testudines, Eucryptodira, Xinjiangchelyidae, phylogeny, Upper Jurassic, Junggar Basin, China. I T has long been known that the Junggar Basin is very rich in fossil vertebrates and it is not surprising that this interesting region has been under study for many years. Much work was done during the expeditions of the Sino-Canadian Dinosaur Project (1987±90). They focused on the north-eastern and central parts of the Junggar Basin, where they collected several complete dinosaurs, turtles and other faunal elements from the Middle Jurassic Wucaiwan and Upper Jurassic Shishugou formations at the Jiangjunmiao and Pingfengshan localities.The new Sino-German Cooperation Project (SGP) (Maisch et al. 2001; Maisch et al. 2003) with teams from the Geological Survey No.1 of Xinjiang, the Nanjing Institute of Geology and Paleontology of the Academia Sinica, the Paleontology Institute of the Jilin University, Changchun, and the Institut fu Èr Geologie und Pala Èontologie der Universita Èt Tu Èbingen started extensive ®eldwork in 2000 around the city of Urumchi, along the southern margin of the Junggar Basin. The main outcrops investigated belong to the Middle Jurassic Toutunhe Formation and the Upper Jurassic Qigu Formation. The only fossil vertebrates hitherto described from this region are the ankylosaur Tianchisaurus nedegoapeferima and associated theropod remains from the Toutunhe Formation near Fukan (Dong 1993).In this paper we describe the ®rst vertebrate fossil, a well-preserved xinjiangchelyid turtle, from the Qigu Formation. It was found west of the Toutunhe River in the Liuhonggou section (Hendrix et al. 1992) approximately 40 km south-west of Urumchi. It clearly belongs to the genus Xinjiangchelys. ...