Very rare shell, perhaps

Many many years ago, I picked up this very small shell (can't remember if it was on a beach in Borneo, Qatar or Oman). I almost threw it back down on to the sand, as it looked rather like a broken piece of a shell, but instead kept it. Some time later, I happened to see a National Geographic Magazine page illustrating some of the rarest shells in the world. One of them looked just like this little one - somewhere around 1" in length, if I remember correctly. Too dead beat to go downstairs to check, after a full day of Christmas Bird Count in the Canmore area (near Banff, in the Rocky Mountains). It's recommended that a person does 10,000 steps a day - well, I've done 23,377 today, LOL, and it feels like it, too! I don't know if someone "out there" is able to confirm or correct this. Would be greatly appreciated : )