Nice Mercury Dime indeed!
That plate with 'rest' marked on it could be a calling card rest from the Victorian era. It looks to be about the right size.
Calling cards were left when a person visited the home of another, to pay condolences, chat, do business, etc. They would have a silver or silver-plated "rest" (or plate-type holder) in the shape of a calling card so that a visitor could leave her card on a table upon leaving. That's my guess as to what your find is, anyhow. Those Victorians had special items for every imaginable use!