What is this steering wheel?

That is a woodgrain steering wheel. It was an installed option on my 66 Dart GT, although the horn button was different. The first couple of photos are definitely 67 & later. On the 66, the horn button had a circular "spring plate" that was attached to the underside of the horn button. When this was horn button was pressed in, the spring plate hooked on to the elevated ring of the horn switch. It was a press-on fit.