Umbonium costatum

Umbonium costatum is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails.

Description
The size of the shell varies between 12 mm and 25 mm. The heavy, solid shell has a depressed shape. Its spire is low-conoidal, the periphery rounded. The color pattern is whitish or light yellow, closely tessellated all over with blackish-olive or reddish-brown squarish spots. The tessellated color-markings sometimes form subcontinuous oblique bands. The surface is shining and polished, with strong spiral grooves above, generally 4 to 6 on the body whorl. The sutures are narrowly impressed, with a rather wide margin below them, which often shows a slight tendency to be tuberculate. The base of the shell is smooth, tessellated around the irregularly convex, flesh-colored central callus. The shell contains six whorls, the last a little concave above, convex beneath. The subquadrate aperture is pearly inside. The circular callus is heaviest in front of the aperture and behind the columellar lip.

Distribution
This species occurs in the Sea of Japan and in the East China Sea.

In culture
In Japan, the snail is called kisago, and its shell was once used as pieces for ohajiki, a children's game similar to marbles.