Agathistoma viridulum is a species of sea snail, a marine gastropod mollusk in the family Tegulidae.

The body whorl is obtusely angulate or rounded at the periphery.

The base of the shell is rather flattened, somewhat concave around the umbilicus, and generally eroded in front of the aperture.

The arcuate columella is expanded above in a bright green callus which partly surrounds the umbilicus, at its base green, bearing a tubercular tooth, followed by several smaller ones.

[2] This species occurs in the Caribbean Sea off Colombia, Costa Rica, Panama and Venezuela; in the Atlantic of Brazil.