Where are my Digital Books Stored?

In the past, books were stored and transferred to iPhones/iPads/iPods via the iTunes library:

However, now it appears they aren't?

I do not want my books stored in iCloud, I want them stored only on my Macbook and iPad.

My book list is now empty (there are still books in my iTunes library, though).

So, where are my books stored in order to transfer to my iPad?

And,

How can I transfer them to my iPad, if not via the interface as shown, and as above, I do not want to be using iCloud for this?

Thank you!

[Edited by Moderator]