Where is float figure* in tufte-book?

[Nikos Alexandris]

Dear Tufte-LaTeX users,

the example file "tufte-book.lyx" contains an example of the "float:
Figure*", a full-width figure box.  I can't trace this anywhere in the
(Insert) menus.

Using LyX Version 2.1.4.  Any help highly appreciated.

Nikos