A "double elephant" Audubon book

Last month I posted a link to information on book sizes ranging from "folio" to "sixty-fourmo."  Not included in that list are the formats that are bigger than your average sheep.  Last week the BBC reported that the "world's most expensive book" was to be sold by Sotheby's - referring to a complete edition of John James Audubon's Birds of America.  It contains life-sized illustrations of the birds, and thus is a huge book.

The BBC article showed only a print, but I located a photo of another copy at the website of the Cincinnati Public Library (embedded above).  It apparently is a "double elephant" folio format [the "elephant folio" is up to 23" tall, the "Atlas folio" up to 25" tall, and the double elephant is 50" tall.]