Sweet little shell shaped dish with removable glass tray inside - I believe this is a butter dish (notch in the lid for a butter knife, or maybe a tiny spoon).
But I think it would also make a nice trinket box to hold your pearls or other jewelry, mermaid style! This measures about 5" x 5" overall.
It's not marked that I could see, probably 50s or 60s vintage? It's not really heavy, or expensive silver - rather cheaply made, with a little spotting and wear to the silverplate.