Kofoid (1911: 228, pl. 13, figs 26, 27)
Dodge (1982: 214, fig. 26A, H), Steidinger & Tangen (1997: 507, pl. 42)
Cells rounded to ovoid, 29–50 µm long, 27–40 µm diameter. Thecae marked with raised longitudinal ridges; epitheca with convex sides and a short apical horn with an apical pore; hypotheca rounded, lacking antapical spines. Cingulum displaced by 2–3 cingular widths, with strong ridges; lists greatly reduced or absent. Sulcus narrow, deeply indented, extending from apex to antapex; sulcal lists ±absent. Chloroplasts present.
Cysts have been recorded from the Southern Ocean; Southern Ocean, near South Georgia (Dodge & Priddle, 1987); Ross Sea (Watanabe, 1982).
Cysts of this species have the palaeontological name Spiniferites bulloideus (Deflandre & Cookson) Sarjeant (Wall & Dale, 1968). These are ovoid, 32-42 µm long, 28-39 µm diameter, with bifid and trifid sutural spines c. 16 µm long.