Large polychelidan lobsters with a rounded carapace from the Middle Jurassic La Voulte-sur-Rhône Lagerstätte: taxonomic clarifications

Polychelidan lobsters (Crustacea: Decapoda) are abundant in the celebrated Middle Jurassic (Callovian) Lagerstätte of La Voulte-sur-Rhône (Ardèche, France). Among them, Eryon giganteus Van Straelen, 1923, is recognized by its large, rounded carapace. The generic assignment of this species has been particularly complicated, with many conflicting assignments proposed since the first description of the species. The present study reinvestigates E. giganteus following the rediscovery of its lectotype. Careful examinations reveal that the type material is composite: the lectotype belongs to a species of eryonid that was described recently as Cycleryon romani Audo, Schweigert, Saint Martin & Charbonnier, 2014, and is quite rare (six specimens); the rest of the material, and most specimens formerly assigned to E. giganteus correspond to an abundant species of Proeryon Beurlen, 1928 (33 specimens) that we herein describe as Proeryon charbonnieri n. sp. The present study also allows us to reinvestigate the generic assignment of E. giganteus. Detailed observations allowed assigning E. giganteus to Soleryon Audo, Charbonnier, Schweigert & Saint Martin, 2014 based upon: the grooves marked across the dorsal part of carapace; a posterior carina near the posterior margin; and a hepatic carina between cervical and hepatic grooves. This taxonomic revision also leads to abandon Proeryon zehentbaueri, the replacement name which was proposed for Proeryon giganteus Beurlen, 1930.