From your picture, this is called a sesame snail

It is a species of the genus Sesame Snail in the family Sesame Snailidae of the order Mesogastropoda. It is also known as the single-toothed snail. The shell is conical, the shell texture is firm and thick, and the shell surface is variable in color. The color of the shell surface is variable, including dark green, white, yellowish-white, pink or brown square spots. Most live in the intertidal zone in the upper zone on the rocks, stone cracks or under the stone.