Key to the species of Masaris Fabricius, 1793

1. Females............................................................................................ 2

- Males (unknown in M. tianshanicus)..................................................................... 5

2. Frons and clypeus covered with dense stiff setae bearing at least small, knob-like, spherical swelling at distal end, forming pollen brush, knobbed setae on frons about as long as diameter of median ocellus (Fig. 12A)......................... 3

- Frons and clypeus covered with less dense setae pointed at distal end, setae on frons much shorter than diameter of median ocellus (Fig. 12B).................................................................................... 4

3. Metasoma black with yellow pattern........................................... M. longicornis (Kuznetzov, 1923)

- Metasoma with reddish pattern at least on tergum II in addition to black and yellow pattern. M. tianshanicus Panfilov, 1968

4. Large species (total body length 15–17 mm); clypeus, frons, dorsal mesepisternum, and propodeum black, metasomal terga I–III completely reddish...................................................... M. gussakovskii Kostylev, 1935

- Smaller species (total body length 10–11 mm); clypeus, frons, dorsal mesepisternum, propodeum, and metasomal terga I–III black with yellow pattern, metasoma without reddish pattern.......................... M. carli von Schulthess, 1922

5. Antennal club long, more or less parallel-sided, apically rather pointed (Fig. 12E); sternum II with acute ventral projection, sternum III with truncate ventral projection, sternum IV concave in posterior half (Fig. 12C); tergum VII rather parallel-sided in posterior half, apically with two carinate teeth and semi-circular emargination between them (Fig. 12F)........................................................................................ M. longicornis (Kuznetzov, 1923)

- Antennal club shorter, more or less broadened towards apex, apically rather truncate (Fig. 12G); sternum II at most bulged, without acute ventral projection, sternum III with ventral projection roundly pointed apically, not truncate, sternum IV not modified (Fig. 12D and fig. 14 in Gusenleitner 2002); tergum VII rather pentagonal, apically without carinate teeth laterally to semi-circular emargination (Fig. 12H and fig. 12 in Gusenleitner 2002).......................................... 6

6. Large species (total body length about 15 mm); sternum II with less produced ventral projection situated posterior to its half-length (fig. 14 in Gusenleitner 2002); tergum VII rather gradually narrowing towards apex (fig. 12 in Gusenleitner 2002)............................................................................. M. gussakovskii Kostylev, 1935

- Smaller species (total body length 10–11 mm); sternum II with more produced ventral projection situated at its half-length (Fig. 12D); tergum VII rather parallel-sided at base and than more abruptly narrowing towards apex (Fig. 12H)........................................................................................... M. carli von Schulthess, 1922