Shell small, slender, more or less cylindrical, white and somewhat diaphanous, with 4,5 slightly to moderately convex, gradually enlarging, teleoconch whorls. Embryonic whorls intorted, with their axis at 135 degrees with the teleoconch axis; their number cannot be determined exactly, because the first protoconch whorl is (partly) hidden in the first teleoconch whorl. Suture simple, not much inclined. Umbilicus closed. Last whorl occupying about 0.6 of the total height of the shell. Aperture oval, somewhat higher than broad; the height is 0.4 of the total height of the shell. Outer lip sharp, neither thickened nor denticulate inside. Inner lip united with the outer lip, sharply, delimited from the body-whorl. Columella concave, with a prominent central tooth. Growth-lines vertical to slightly prosocline. The shells are 1.6-1.95 mm high and 0.75-0,9 mm broad in Getares. Specimens from N. Africa remain smaller and are slightly more slender, reaching 1.65 mm in height and 0.7 mm in breadth.

O. kromi is a rather variable species, which in most of its forms resembles O. plicata (Montagu, 1803). In the latter species, however, the embryonic whorls are helicoid, with their axis at 90° with the teleoconch axis; the entire protoconch can be clearly seen from the outside.

DISTINCTIVE FEATURES:
• Shells with a clear tooth on the columella.
• Shell surface smooth
• No (spiral) ribs.
• Inside of the outer lip smooth.
• Embryonic whorls of type B, somewhat tilted.
• Growthlines more or less vertical.
• Shell-surface shiny in appearance.
• Shell small (1,8 mm)
• Shell with (usually) well-rounded whorls.
• Spiral not turriculate.