Pearly Mussels

America has these  "Pearly Mussels" in rivers which have been dying out due to pollution in rivers among other things -

I found these and scrubbed them for gifts.

Read more reports and learn more about the history of these pretty shells here.
http://www.nysm.nysed.gov/pubsforsale/detail.cfm?pubID=5222
http://images.google.com/search?q=MARGARITIFERA+MARGARITIFERA&biw=949&bih=609&sei=a4UGUdqzDeyw0QHQ2YHYCw&tbm=isch
http://www.animalbase.uni-goettingen.de/zooweb/servlet/AnimalBase/home/species?id=2308


This is a photo of buttons that were stamped out from these shells.