I write the name of the shells if I know it. Otherwise I write the maximum details about it, so it can be named after.
I write the size, where as in Country, City, Town and name of the beach or reef, if in sand or on rocks, then the depth, water temperature and the date.
I also have plastic sealed bags of different sizes that I can write a note like the date, the place and leave it with the shell. And later, at home I will be able to find the right name.