Sinemys lens is redescribed on the basis of new material from the Early Cretaceous of Shandong, China, and a new species of Sinemys from the Ordos Basin in Inner Mongolia is recognized. Sinemys and Manchurochelys are placed in the Sinemydidae (sensu stricto) on the basis of the derived features of a small first suprapygal and an elongate, narrow posterior lobe of the plastron. Sinemys is autapomorphic in the absence of a cervical scute, the entry of the first vertebral onto the anterior margin of the carapace, the absence of a pygal bone, the entry of the fifth vertebral scute into the posterior margin of the carapace, in that the riblike lateral projections of the last three costal bones fit between the adjacent peripherals, and in the isolation of the epiplastra from the hyoplastra by lateral expansion of the entoplastron.Sinemys gamera sp.nov., from the Early Cretaceous Luohandong Formation of the Ordos Basin, Inner Mongolia, is characterized by the presence of a flat carapace with an abbreviated posterior end and the presence of long spines on the seventh costal. The spines in S. gamera may serve a hydrodynamic function.

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