Help please with identification

[vaigret]

I have found a shell on Mablethorpe beach , England and need help in identification. It is nearly round about 1 inch in diameter. It is very thin and brittle. It has a very small hole on the bottom. On the top it has three raised ridges all defined from each other by rows of double lines of dots as well as a groove which comes from the middle of shell down to the hole at the bottom.

I cannot see a picture of it anywhere on the site. Help please