G.Karst. (Karsten, 1905: 78, pl. 5, figs 9, 9a)
Cells (presumably) discoid. Valves circular, 82–86 µm diameter. Areolation fine, radially fasciculate; marginal band of areolae 4–5 µm wide. Spines in 2 regular rows near the marginal band; spines of outer row longer than inner.
Southern Ocean, Indian sector (Karsten, 1905).
Priddle & Fryxell (1985) reported and illustrated C. horridus from the Southern Ocean, but they noted that the material was probably referrable to Thalassiosira (Thalassiosiraceae).