Castrac. (Castracane, 1886: 77, text fig.)
Mangin (1915: 36, figs 15, 16), Hendey (1937: 294), Hustedt (1958: 135)
Cells usually solitary, sometimes united in short chains of 2–6 cells, ±rectangular in girdle view, heterovalvate; pervalvar axis 10–15 µm. Valves elliptical to circular; apical axis 15–36 µm diameter; upper valve convex; lower valve flat or concave. Setae emerging from centre of valves, those of upper valve distinctly separate and abruptly reflexed, those of lower valve divergent and lying ±parallel to upper setae. Chloroplasts small, numerous.
Southern Ocean, south of Australia; South Atlantic at 51°29’S 0°08’W (Hustedt, 1958); Petermann I., Bransfield Strait (Mangin, 1915); temperate South Atlantic and around the coasts of South Africa (Hendey, 1937).