I bought this knife (see pics) several years ago and, truth be told, I really was not, and am not sure what it is. It is marked on the blade:
Made in France
I know it is from the Professional Sabatier line and I believe it was made for the American market, mainly due to the fact that it says stainless on the blade rather than INOX. It is 5 1/4" long and 1" wide.
I do not think it was intended to be an oyster knife because it is quite thin and has a very sharp edge. It may have been made for clams, but usually they are longer and thinner. I wonder if there are any existing catalogs that document what it is for. Any help would be greatly appreciated.