Note on the synonymy of Davidius ater Hagen in Selys, 1878 with D. nanus (Selys, 1869) (Anisoptera; Gomphidae)

We recently noticed that the Japanese taxon Davidius ater Hagen in Selys, 1878 has generally remained listed as a valid species in recent world Odonata catalogues. Its retention is an artefact of the rather complicated taxonomic history of the Japanese Davidius taxa. In his “Les ©donates du Japon”, the first synopsis of the Japanese odonates, E. DE SELYS LONGCHAMPS (1883, Annls Soc. ent. Belg. 27; 82-143) lists two Davidius species, ‘Davidius nanus Selys’ and ‘Davidius ? ater Hagen’ referring to the original descriptions. The former species had been described by Selys as Hagenius ? nanus from a single female specimen from “Japon” in E. DE SELYS LONGCHAMPS (1869, Bull. Acad r. Belg. (II) 28; 168-208 and the latter by Hagen on the basis of incomplete (tips of abdomen missing) male and female specimens from Jeddo [Tokyo] in E. DE SELYS LONGCHAMPS (1878, Bull. Acad. r. Belg. (11)46:408-471,658- -698). Then E. DE SELYS LONGCHAMPS (1894, Annls Soc. ent. Belg. 38: 163-181) described a specimen as “the first male” of D. nanus, but later this was proven to be nonspecific with D. fujiama Fraser, 1936 (S. ASAHINA, 1957, Shin-Konchu 10[6]: 51-58), F. RIS (1916, Supplta entomol. 5: 1-81) described a new species D. cuniculus based on both sexes from “Shoji, Plateau des Fujiyama”; this species was subsequently synonymized with D. nanus by S. ASAHINA (1950, Iconographia insectorum japonicum, editio secunda reformata, Vol. 3, pp. 131-168). Ris also described and illustrated a female specimen as D. ater, but according to ASAHINA (1957, loc. cit.) this was the same as Lanthus fujiacus, a species described by EC. FRASER (1936, Trans. R. ent. Soc. Land. 85: 141-156). In the same paper Fraser, in his turn, wrote “I am inclined to regard D. cuniculus as the real D. ater Selys, but as the end of the abdomen of the type male and allotype female are both missing, it is impossible to be certain”. A further taxon, Gomphus hakiensis, described by a single female by S. MATSUMURA in K. OGUMA (1926, Ins. matsumur. 1 [2]: 78-100, 1 pi, excl.) was first synonymized with D. cuniculus by K.J. VALLE (1941, Annls ent. fenn. 7; 141), later with D. nanus by ASAHINA (1950, loc. cit.).