The valve is elliptical with convex margins and bluntly rounded apices. The valve length is 34.5 μm and the valve breadth is 15.5 μm. The axial area is narrow and lanceolate, expanding into a large elongate central area. The central area is elongate-oval, 4.5 μm wide. The longitudinal canal is lanceolate with two rows of areolae in the middle of the valve, gradually narrowing into one row toward the valve apices. The raphe is straight and simples, positioned with an expanded depression. The striae are uniseriate and radiate, 18 in 10 μm, composed of round to rectangular areolae, 12 in 10 μm.

Observations:— Diploneis mongolica was described by Metzeltin et al. (2009) from Lake Khangal, Mongolia. The type material of D. mongolica was observed and compared with the specimen from Arkhangai region. In contrast to the type population, where D. mongolica is quite dominant, in Arkhangai region this taxon is extremely rare with only one specimen found. Even though larger valves of the given size range were not observed, the observed specimen fully fits the original description given by Metzeltin et al. (2009).

Ecology and Distribution: —M166A; M167A: examined for comparison, not found in Lake Hövsgöl but distributed in lakes and streams in Arkhangai and Khentii provinces (Metzeltin et al. 2009).