(From Anquetin et al. 2017:330): Achelonia formosa is based on two specimens from the late Kimmeridgian locality of Cerin, France (Meyer 1860). The first specimen (MHNL 20015606) consists of a fragment of the anterior rim of a carapace (partial nuchal, left peripherals I–III, and partial left costal I), parts of the pectoral girdle, remains of the left forelimb, and a crushed skull. The second specimen (MHNL 20015608) consists of two manus exposed in palmar view on a slab of limestone. In a relatively ambiguous statement, Meyer (1860) noted that Victor Thiollière, who communicated this material to him, declared that the two specimens were found at the same time and belonged to the same turtle. It is rather unclear, however, whether Thiollière and Meyer were suggesting that the two remains belong to the same individual or simply pertain to the same species. Rütimeyer (1873a) referred the two specimens to the same taxon, whereas Lortet (1892) clearly stated that the aspect of the sediment suggests they belong to the same animal. However, it is difficult to confirm whether or not the two specimens belong to the same individual since there is no connection between the slabs. For clarity, we designate the first specimen (MHNL 20015606) as the lectotype of Achelonia formosa.

Achelonia formosa was named by von Meyer (1860). Its type specimen is MHNL 20015606, a partial skeleton (fragment of the anterior rim of a carapace plus associated partial left forelimb and skull), and it is a 3D body fossil. Its type locality is Cerin, Jura, which is in a Kimmeridgian terrestrial horizon in France. It is the type species of Achelonia.