| ABSTRACT: | A new fossil turtle specimen from the Late Jurassic of Solnhofen, Germany, provides new insights into the validity of the species Palaeomedusa testa. The new specimen exhibits a number of characters in the carapace, such as the absence of well-developed fontanelles and the presence of three cervicals, five pleurals, and narrow vertebrals, which are present in Palaeomedusa testa, but not in Eurysternum wagleri. These characters warrant the tentative placement of the new turtle in Palaeomedusa testa and the refutation of the traditionally accepted synonymy between Eurysternum wagleri and Palaeomedusa testa. An additional taxon, Thalassemys marina, is also cautiously placed in Palaeomedusa testa, thus synonymizing Thalassemys marina with Palaeomedusa testa. The presence of three cervicals and a wide, trapezoidal nuchal is currently thought to be diagnostic of the Plesiochelyidae and Eurysternidae, respectively, but both characters occur simultaneously in Palaeomedusa testa. Consequently, one of these characters must have been lost during phylogeny or evolved twice and therefore is not useful in diagnosing a monophyletic group of turtles. Finally, the fossil taxon Eurysternum wagleri, which is primarily diagnosed by its deep pygal notch, is based on the description of an illustration of an incomplete and now missing fossil turtle specimen. Although the designation of a neotype may be useful, this study demonstrates that no eligible specimen is available, and as such, the type illustration will have to suffice until a neotype is found.
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