S. Mahunka szerk.: Folia Entomologica Hungarica 44/2. (Budapest, 1983)

into account the average elevation above sea level (1580 m), this area belongs to the uppermost situated ones in the world. The average altitude of our localities is 1292 m a.s.l. Mongolia' s territory consists of two principal physiogeographical units defined by its morphostructure, prevailing geomorphological processes, lithological particularities and hydrological conditions, climate, and vegetation. All these components affect the aquatic biotopes as well. As pointed out by several authors dealing with aquatic insects, the southern part of Mongolia belongs, according to its characters, to Central Asia, while the northern one to Eastern and Southern Siberia (see RAUÍ3ER, 1968 for details). The localities investigated are evenly distributed throughout the Mongolian territory except for the waterless area of the Gobi desert (Fig. 1). Most localities are situated in the northern part of the Gobi area (A) in dry steppes of clean-cut continental type (14 localities) and in the desert of clean-cut continental type in the Intramountanious basin (Ab) (4 localities). Nine localities (see Fig. 1) are situated in the semideserts and steppe thin forests of the Altai Mts. (C) and Dzungaria (D). The remaining localities are situated in the Khangai Mts. (B) (8 localities) and in the Hind Baicalian Highlands (D). The last area is closely connected with Siberia from the physico-geopraphical point of view. Twenty-one localities are situated in the basins of three principal rivers: Selenke (Selenga, Baykal Lake or Yenisey basin), Tola and Kerulen (Amur basin). Further localities are situated in desert or semidesert areas with an extremely dry climate and there is no doubt that the mayfly larvae inhabit also periodic aquatic habitats at these localities. For further details concerning physico-geopgraphic features and localities, see e.g. KAS7AB (1965), RA US ER (1968) and others. There are 41 localities at which Ephemeroptera species were collected during Dr. KASZAB'

s expeditions. The localities are situated at altitudes of 585 - 1900 m. The material comes from various administrative districts (aymaks) as follows Archangal; Bajanchongor; Bayal Ölgiy; Bulgan; Central; Chentei; Chovd; Chövsgöl; Coybalsan; Gobi Altai; Suchebaator; Uvs. SYSTEMATIC PART Siphlonurus alternates (Say) (Fig. 3) Material examined: Archangai aymak, 24 km N of Somon Lun, 1520 m, July 1, 1964 (No. 238), 1 ?; 8 km W of Somon Urdtamir, Khangai Mts, 1680 m, July 21-22,1966 (No. 723, 724), 1 Ç . This circumpolar species is recorded for the first time from Mongolia. Only females comprised our material. Subgenital plate of sternum VII is slightly more produced (Fig. 3) than that in European populations, but according to our opinion this variability does not exceed species range. BRODSKY (1930) records this species from Novosibirsk, BRAASCH (1982) from the vicinity of Khabarovsk. There is no doubt that occurrence of this species in Mongolia represents an arctoalpine disjunction to Central Asia. Siphlonurus lacustris Eaton (Fig. 2) Material examined: Chövsgöl aymak, Tesiin gol riv., Alag Mort, 42 km NE of Pass Chaldzan Sogotyn davaa, 1900 m, July 15, 1968, light trap (No. 1109, 1110), 1 o. This species is recorded from Mongolia by BRAASCH (1982) and from the Far East (Amur basin) by TSHERNOVA. LEVANIDOVA (1982) found S. lacustris also in Chukotka and Kamchatka. Our female resembles that of S. chankae (this species is known from the Amur basin and the Muren gol riv. in Mongolia - TSHERNOVA, 1952; BAYKOVA & VARYCHANOVA, 1978) but is distinguished by smaller body size and different colour patterns. BAETTDAE Baetis fuscatus (Linnaeus) Material examined: Chovd aymak, Bulgan gol riv., 10 km SSW of Somon Bulgan, 1200 m, July 4-5, 1966 (No. 628, 629), I cT, 37 Ç; Gobi Altai aymak, Mongol els, 10 km SE of Somon Chechmort, 1600 m, July 13, 1966, light trap (No. 684), 1 c?; Chövsgöl aymak, 6 km WNW of Somon Tosoncengel, 1400 m, June 18, 1968, light trap (No. 981), 1 $; Tesiin gol riv.,