Hagen’s tubercle, a largely overlooked but potentially useful character in gomphid taxonomy (Anisoptera: Gomphidae)

HAGEN’S interesting comments on the shape of the ventral surface of the first abdominal segment in the males of the “Légion Lindenia contributed to SÉLYS’S “Monographie des Gomphines”, have been overlooked by most later workers. Diastatomma tricolor (Palisot de Beauvois), in which the “tubercule" on this segment is spectacularly developed, was only known in HAGEN’S time from a single specimen in which half this segment was missing, so the tubercle is not mentioned. More material is now available for study, and the genera Diastatomma, Gomphidictinus and Gomphidia are discussed in the light of this.