I live in a farm house built in the 1930's. One of the bedroom doors has a strange latch on the door. It's built into the door, like modern latches, and retracts when you turn the handle to open the door. Most latches have a curved face on the side that hits the strike plate and a flat side on the reverse. The flat side catches against the strike plate to keep the door from opening.
What's unusual about this one is that both sides are curved. From the top, it looks like an arrowhead. Without a flat side, it allows some play so that the door rattles when closed if there's a breeze. The only advantage to this design that I can think of is that it could be used in a door that swings in and out. Anybody else ever seen one of these or know what good they are?