The second book structure from 'Woven and Interlocking Book Structures' by Claire Van Vliet and Elizabeth Steiner - this one is called 'Moeraki Boulders'. Six individual pages are held together with binding strips and a series of slots and tabs. It took me a while to work out the correct sequence for the binding, but after a bit of trial and error I finally got there. The original version of this book was apparently made with circular pages and circular tabs, hence the name.