Eunotia rabenhorstii var. monodon Cleve & Grunow

in Van Heurck, Syn. Diat. Belg., pl. XXXV, fig. 12B. 1881.

(Figs. 76, 77)

Valves with dorsal margin convex with an attenuatedrounded undulation in the middle region, ventral margin concave. Ends rounded, widely dilated. Striae parallel to radiate towards the ends. Length: 9.0-25.5 μm; width: 5-9 μm; striae 13-16 in 10 μm. E. rabenhorstii var. monodon resembles E. rabenhorstii var. triodon Cleve & Grunow, differ by the number of undulations on the dorsal margin. E. rabenhorstii var. monodon presents one undulation while E. rabenhorstii var. triodon has three undulations on the dorsal margin (Van Heurck 1881). The specimens observed are similar to those registered by Costa et al. (2017).

Material examined: BRAZIL, MATO GROSSO DO SUL: Taquaruçú, Patos Lake, 23.III.2018, sediment, D.T. Ruwer (Nupélia UEM - 18098, 18101-102, 18104, 18106-107, 18109-111, 18113-121.

Occurrence: first citation for Upper Paraná River floodplain.