I think I'm only asking this for confirmation, rather than because I don't know, but the last couple of books I've read have featured a few instances where a quick dialogue between two people has been in the same paragraph. My reasoning is that this is done when the story-teller wants to quickly explain a short dialogue that took place, rather than bother setting it out with the normal formatting of a new line for each speaker. Almost as though it's done as an aside. Example from one of the books: 'Good news?' she said, because I owed her so much rent. 'You never can tell,' I said. 'But it's from a great man. He could send blank pages, and it would be good news to me.' There's other examples where the exchanges go on for even longer, but I can't remember where they occurred.