Dave are you there, I need your help with another shell PLEASE

[dave r]

Yes, he is correct. The "litle shell inside" you describe is in fact the operculum, this is like a little 'trap-door' that several species of shell have. It closes the opening behind them when the animals retract into the shell. It is customary to glue the operculum of the shell to a piece of cotton wool and put it into the aperture.
I think the little data labels that came with the shells may have got mixed-up at some point. You need to be very careful in future sales.
There is a very good website called 'Hardy's internet guide to marine gastropods'(type this into your search engine) run by my friend Eddie Hardy, you could use this to check the names on the labels before you sell them by matching the specimen with the photo on the website.
If you need any more help give me your email address and I will get in touch.
Dave.