Agardh (1824: 1)
Smith (1853–56: 27, pl. 37, fig. 301), Boyer (1927: 232), Hendey (1951: 41, pl. 16, figs 9, 10), Hustedt (1958: 143), Hendey (1964: 174, pl. 28, figs 7, 8), Andreoli et al. (1995: 472, fig. 5)
Cells solitary or chain-forming, attached by valve surfaces, heterovalvate, genuflexed in girdle view on the transapical axis; apical axis 29–90 µm; transapical axis 30–40 µm. Valves linear to elliptical; lower valve concave, with a raphe; upper valve convex, with a slightly eccentric pseudoraphe. Transapical striae straight, uniseriate; poroid areolae 7–8 in 10 µm; poroids with complex cribra. On R-valve, the transverse area around the inner raphe-ends is non-areolate (fascia) (Fig. d). Girdle structure composed of punctate annular segments. Chloroplasts usually 4 irregular or elliptical bodies arranged in pairs around the girdle (Hendey, 1964).
Plough I., near Davis Station, Prydz Bay, East Antarctica; Ross Sea (Watanabe, 1982); Terra Nova Bay (Andreoli et al., 1995); Kerguelen Is. (Heiden & Kolbe, 1928); cosmopolitan, Great Britain (Hendey, 1964).
Material collected from coastal waters near Davis Station in the current study has smaller cells (apical axis 29–61 µm) than those of previous reports.