I always thought that the insides of mussel shells were pretty even though the outsides tend to be a bit ugly.  I saw a post here where someone had made these into flowers.  Seeing as there are literally hundreds of these right across the street from my house, I figured I would give it a try.

I'm not quite sure how the original ones were made or what I will do with my completed flowers, but here are the steps on how to complete them:

1. Gather 5 shells that are all about the same size.
2. Assemble them in the shape of a flower
3. Glue them together one shell at a time (I used hot glue)
4. Allow shells to dry completely before gluing the next one (otherwise they will fall apart easily)

Notes and Tips:
1. Make sure the shells are washed and thoroughly dried before you start.  If they are dirty or wet the the flowers will fall apart.
2. Experiment with different shapes and sizes of shells

All in all these were very easy to make, the key is just to be patient in letting the glue dry.  Other glue may work better than hot glue, but I found that mine have held together just fine.

Here are some similar ideas I found that you can try using the same materials and techniques:
https://www.etsy.com/listing/158061738/coastal-shores-extra-large-blue-mussel?ref=market
https://www.etsy.com/listing/187368251/xs-mussel-shell-wreath?ref=market
https://www.etsy.com/listing/107675972/maine-mussel-shell-wreath?ref=market
http://www.rimonthly.com/Blogs/ridaily/December-2011/Oh-Mussel-Tree-Oh-Mussel-Tree/