Diloma concameratum, common name the speckled periwinkle, is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails.

The very thick and solid, imperforate shell has a globose-conical shape and is generally rather depressed.

The body whorl slightly descends at the aperture and is not eroded on the base.

The outer lip is margined within with yellow and black, followed by a nacreous and then by an opaque white thickening which more or less contracts the aperture and which is more or less notched at about the place of the periphery.

The more prominent characters of this species are the strong spiral ribs and the thick outer layer of yellow and purplish-black, or of black veined with yellow, which usually assumes a tessellated pattern.