Enhanced eBook to appear as Audiobook in iTunes?

Hello,

I just bought a book on iBooks called "The Crown of Ptolomy" by Rick Riordan. It is advertised as "enhanced" including an audio recording reading of the book by the author. When I bought the other two books in the series (Son of Sobek and Staff of Serapis) the audio versions of the books have appeared as audiobooks in iTunes, but this one has not. I don't remember doing anything special for them. How do I get this book to appear in iTunes so I can listen to it on my phone? Or maybe there's another way to listen?

Thanks a million to whomever could help me with this one.

Leo