Ding dong...the door bell's broken

I have absolutely no idea how to make this thing work. In an attempt to do something productive today I tried to work on the door bell. This is a real old school doorbell and the only one I have ever seen up close. I have no idea when these were common, but I'm pretty sure its been there for a long time. Its in the doorframe in our living room. I unscrewed it, but can't get the cover off. I don't want to hurt the wood or the bell, so I have no idea what to do. I don't know why, but it's driving me crazy that it doesn't work! We don't even use that door because of this

Those are skeleton keys. Which puts this door out of commision, but is one of the coolest things I've ever seen. I have never been in a house that has these...at least a house that still had the keys. I haven't seen a mention about it in any other blog either.

Oh...the wood was stained and beautiful when we bought the house. Those scratch marks are courtesy of our black lab Cledus trying to see whats going on when any one pulls in our driveway. Our floors and one window also look like this now :(

Once I get something figured out about this I'll share