Help, fossil, coral reef, sea related item???

About half way through my 30 year Greek Island holiday history a Greek resident showed me one of these items. He said they were called the "eye of the sea" and bestowed good luck on the finder of these rare items. I now spend most of my time on holiday looking for these elusive items on the beach (keeps me away from the sun tan boredom and I have found other interesting items in the process - much better than chilling on a sun bed). But I would really like to know exactly what these items are - any help would be appreciated.
The attached photo shows the front and reverse of one of these items - any help would be much appreciated.
Regards, Jays

I'm not sure, do you think we could have a larger picture? ;)

How big is it? Looks like a gastropod (marine snail) to me. Have you seen the animal that lives in it? Guess not if it's rare.

Thanks for reply - god knows why the photo is so big, it was only a thumbnail size when I loaded it!! Anyway, the size of these items vary, from approx just over half a cm to as large as 2 cms. One side always has the white spiral finish with the other side being various shades of peachy/brown.

Hi

Are they solid or hollow?

Is there an opening into them.

From looking at the pictures, they almost seem like part of a shell, the rest having worn away by the sea.

How thick are they?

I've been raking around ebid and ebay in the shell category, took me ages, but I have finally found that these items are generally known across the world as Shivas Eye (of the sea) shell. They apparently come in several shades ( and sizes) on one side from beige to green (depending on their location in the world), with the reverse always being white/ivory with the swirl effect depicted in the above photo. They are generally used as jewelery items. Thanks for your help, I'm going back to Greece to find some more soon - it passes the time and provides a much better sun tanning process than lying on a sunbed.
Regards,
J
http://uk.ebid.net/stores/Jays-Collectables-and-Gifts