The signipennis-group and testaceiceps-group of Rhaconotus (Hymenoptera: Braconidae: Doryctinae) in Vietnam, with descriptions of new species

This study revises the taxonomy of the genus Prismognathus Motschulsky, 1860 (Coleoptera: Lucanidae) endemic to Taiwan. To resolve nomenclatural ambiguity, the author designated a neotype for P. formosanus Nagel, 1928, whose type specimen has been lost. Morphological and distributional analysis confirmed that P. piluensis Sakaino, 1992 represents only intraspecific variation, leading to the new synonym: P. formosanus Nagel, 1928 = P. piluensis Sakaino, 1992, new synonymy. Furthermore, examination of the holotypes determined that P. davidis nigerrimus Sakaino & Yu, 1993 is a junior synonym of P. davidis cheni Bomans & Ratti, 1973, confirming that color polymorphism alone is insufficient for subspecific division. This revision clarifies the classification of Prismognathus in Taiwan.