I was walking the dog around a reservoir, I know well. [my entire life] in a very nice broadleaf woodland. Had my shades on, and thought at first that some kids or something had smashed a load of fancy dinner plates into small pieces on the path. They had that mother of pearl look. Bit further on, I realised they were doing some work, had drained about a metre of the reservoir, and they were literally hundreds of smashed shells of freshwater clams, or molluscs, scattered around the edges of the path. Some had obvious beakholes in them, and the crows had been feeding on them. Looked identical to this. Never seen them before. How do you prepare them,and are they tasty? Do I have to put them in freshwater, and sprinkle oatmeal in the water, then leave for a couple of days? to filter out the crap? Ive seen them do that with sea clams, then just put them on the embers of a fire to open?