Diagnosis. Spiral and ⁄or annular arrangement of depressions showing a characteristic arched or suboval outline. Furrows connecting depressions absent.

Description. Depressions either spiral or spiral-annular in arrangement (Text-fig. 2B–C, Pl. 1, figs 7–8). This makes the trace appear as more or less circular, isolated groups of depres sions with a total diameter between 4 and 10 mm. During the initial stages, depressions are consistently arranged in spirals and show a subcircular outline. In later stages, they develop a very characteristic arched or suboval outline (Pl. 2, figs 1–4), and their arrangement either remains spiral or changes into annular. The centres of the depressions are deeper than the outer parts (Pl. 2, figs 3–4). Depression width varies from less than 0.1 to 0.1 mm in the smaller ones, and from 0.1 to 0.3 mm in the larger. In some instances, a very shallow and often indistinct, outer furrow is present, ranging from 40 to 60µm in width.