I'm seriously spamming my own thread. Just wanted to show my shell sorting operation I have going in in the living room.
I have 7 bags where I sort the shells into 7 different sizes. Of course, the sizes are a gradient, but I can usually fit them into one size bag or another without too much trouble.
You can see I have many hundreds to go.
It takes about 10 seconds to check one shell. First, I stick a needle inside to see if I accidentally got a live or fresh dead snail at the time of collection. If that is the case, the needle will hit an operculum, and I will toss the shell into the non-use bag. If the needle hits nothing, I check the outside of the shell for holes. Sometimes, the shells are so small, it's hard to tell if there is a hole or just a discoloration. The needle comes in handy there, too.
Here is a closer pic of the shells. Most are sitka periwinkles, but they are "turbo-like" so I thought the crabs would like them. I got them in Juneau/Auke Bay Alaska last summer. I once sat for hours at a popular tourist spot getting shells, and tourists kept thinking Tiger (my dog) was a bear! lol! He was sleeping in the beach grass, so you could only see a huge brown furry thing.
They are seriously my babies now. I hatched a chicken once, and it was the best thing ever and then it died a few months later because it had some sort of disease where one of it's legs stuck out sideways. 
I take anywhere from 200-400 pics per session, and when I'm done editing, I am usually left with somewhere around 20. So I take many more bad pics, than good pics.