Diagnosis. An Oichnus that abruptly changes diameter from wide externally to narrow internally. The two parts are concentric.

Description. Diameter of the externally and internally situated parts ranges from 4 to 15 urn and from 1 to 7 urn, respectively. The margin of each component is perpendicular to the external surface of substrate. At the transition from the proximal to the distal component the margin is parallel to the surface of the substrate. O. gradatus isp. nov., which is present in samples from the Red Sea (sample Nueba 1), West Greenland (sample E6), Great Australian Bight (sample G 558) and Rhodes (P34), occurs in both benthic and plank tonic foraminiferan.

Diagnosis – (After Nielsen & Nielsen, 2001, p. 110.) “An Oichnus that abruptly changes diameter from wide externally to narrow internally. The two parts are concentric.”
Description – Non-penetrative (failed), elliptical borings that change diameter in external width, averaging 90 μm longest diameter and 75 μm shortest diameter, to narrow internal width, c. 30 μm. The margins of both parts are perpendicular to the substrate surface.

Emended diagnosis:Sedilichnus having openings of regular to irregular elongate-oval outline. The margin is perpendicular to the substrate surface; the walls in the distal end are straight or slightly rounded (after Nielsen and Nielsen, 2001).