Ghost books - where on my ipod??

I just did a sync on my ipod touch 4g and had a bit of a clear out to make a little room. I noticed that it's saying there are around 15 books on there. I can't find them anywhere on my ipod, nothing comes up when I search the device for the titles, and there's nothing stored under BOOKS. Oh, and I have no book apps.

I deleted all the titles from my iMac, but when I did my sync, it's copied them all back over from my ipod.

This is driving me crazy!! How do I find & delete these books when the ipod is saying they're not even there!!??

Thanks.

 

Nope. I don't have any book apps on the ipod.