iTunes changed some epub ebooks into audiobook format.

iTunes has changed some epub ebooks into audiobook format. They are obviously broken in this state. How do I change them back? This is iTunes 12.2.25 and OS X 10.10.5. It did not do this with all the books, but with several dozen. The change may have been coincident in time with an over-wifi sync with my iPhone-6, but I'm not sure.