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Slight variation is apparent between eastern (Tisza) and western (Gyöngyös, Rába) populations of O. rhenana in the shape of abdominal segments 8 and 9 (Figs 3-4). These segments of the western populations are similar to those of O. marichuae Alba Tercedor, 1983. However, the vestiture of the basal half of posterior margin of middle and hind femora is typical to O. rhenana. Alba Tercedor (1983) distinguished larvae of O. marichuae on the basis of shape of abdominal segments (see Alba Tercedor 1983: Fig. 18) and vestiture of basal posterior margin of middle and hind femora. Acknowledgements — The authors wish to thank Adam Glazaczow and Tomas Soldán for the valuable information as well as Gy. Sziráki for his help in solving problems about the adult mayflies and for providing the material deposited in the HNHM. Thanks are also due to O. Merkl for comments on and translation of the text. REFERENCES Alba Tercedor, J. (1983): A new species of the genus Oligoneuriella (Ephemeroptera: Oligoneuriidae) From Spain. —Aquat. Ins. 5: 131-139. Hägen, H. A. (1855): Die Ephemeren-Gattung Oligoneuria. — Stettin, ent. Ztg. 16: 262-270. Keffermüller, M. (1964): Uzupehiienie badan nad faunajçtek (Ephemeroptera) Wielkopolski. — Badan. fizjogr. Pol. zachod. 14: 69-86. Kluge, N., (1997): Ephemeroptera. — In: Tsalolikhin, S. J. (ed.): Key to freshwater invertebrates of Russia and adjacent lands, Vol. 3. Zoological Institute of Russian Acad. Sei., St. Petersburg, 176-220, pi. 8-20. [In Russian.] Kovács, T., Ambrus, A., Bánkuti, K. and Juhász, P. (1998): New Hungarian mayfly (Ephemeroptera) species arising from collectings of larvae. —Miscnea zool. hung. 12: 55-60. Mocsáry, S. (1899): Ordo. Pseudo-neuroptera. — In: A Magyar Birodalom Állatvilága (Fauna Regni Hungáriáé). A. K. M. Természettudományi Társulat, Budapest, pp. 23-27. Mol, A. W. M. (1984): Oligoneuriella polonica n. sp., and a note on O. pallida (Hägen, 1855) (Ephemeroptera: Oligoneuriidae).— Ent. Ber. Amst. 44: 126-128. Pongrácz, S. (1914): Magyarország Neuropteroidái. (Enumeratio Neuropteroideum Regni Hungáriáé.) — Ro vart. Lap. 21: 109-155. Russev, B. and Vidinova, Y. (1994): New representatives of the order Ephemeroptera (Insecta) for the fauna of Bulgaria. — Lauterbornia, 15: 85-87. Soldán, T. (1978): Mayflies (Ephemeroptera) new to the fauna of Czechoslovakia found in 1972— 1977. —Acta ent. bohemoslov. 75: 319-329. Sowa, R. (1973): Contribution à l'étude des Oligoneuriella Ulm. européennes (Ephemeroptera, Oligoneuriidae). — Bull. Acad. pol. sei. (Sei. Biol.) 21: 657-665. Sowa, R. (1975): Ecology and biogeography of mayflies (Ephemeroptera) of running waters in the Polish part of the Carpathians. 1. Distribution and quantitative analysis. —Acta hydrobiol. 17: 223-297. Sziráki, Gy. (1995): Adatok a Dráva-mellék kérész (Ephemeroptera) faunájának ismeretéhez. (Contribution to the knowledge of mayflies (Ephemeroptera) of the Dráva Region, Hungary.) — Dunántúli Dolg. Term. tud. Sorozat, 8: 37-39. Sziráki, Gy. (1998): A Dráva mente kérész (Ephemeroptera) faunája. (The mayfly (Ephemeroptera) fauna of the Dráva region, Hungary.) — Dunántúli Dolg. Term. tud. Sorozat, 9: 131-134. Újhelyi, S. (1959): Kérészek-Ephemeroptera. — In: Magyarország Állatvilága (Fauna Hungáriáé), V, 5. Akadémiai Kiadó, Budapest, 96 pp.