Revision of the enigmatic snake Plesiotortrix edwardsi Rochebrune, 1884 from the Phosphorites du Quercy, France

Plesiotortrix edwardsi Rochebrune, 1884 was one of the first snake taxa to be described from the Phosphorites du Quercy, France. The taxon was established in the second half of the 19th century, based on three articulated vertebrae that were found in an unknown locality in the area of Quercy. Originally, only a brief description was provided coupled with a lithograph that depicted the holotype specimen in anterior and dorsal views. Nevertheless, Plesiotortrix Rochebrune, 1884 has since frequently appeared in ophidian literature across the past 140 years and even emended diagnoses have been proposed, but still, its exact affinities have been obscure. I investigated the holotype and only known specimen and I am herein providing, for the first time, photographs and detailed comparisons with other snakes. Several inaccuracies are identified among the original lithograph and the actual specimen, which have inevitably affected past anatomical comparisons and taxonomic interpretations. Plesiotortrix is probably belongs Constrictores but a more precise, family level, determination is not possible. Moreover, the incompleteness of the holotype and only known specimen, coupled with a totally unknown intracolumnar variation of the taxon, lead me to consider Plesiotortrix edwardsi to be a nomen dubium.