Acid preparation, at the Natural History Museum, London, of a turtle skull and jaw presented to the Museum of Geology, Sandown, Isle of Wight, England, by R. W. Harris in 1931, has revealed extremely derived palatal morphology previously undescribed in turtles. The specimen is described as a new genus and species, Sandownia harrisi, and is superficially similar to certain soft-shelled turtles (family Trionychidae) although the extensive secondary palate and extensive skull roof are previously unknown for this family. Other features of the skull suggest that it is not a trionychid but can be assigned to the Trionychoidea and that its closest affinities are with the members of the Trionychia (Carettochelyidae and Trionychidae). This specimen is one of the oldest known cryptodiran turtles that nests within the living families (the Polycryptodira). It suggests that the deep divergences among the living families of the Cryptodira occurred more than 110 million years ago.