There are several pages in the 19th-century photo-album assembled by the London optician Richard Willats that are missing the photographs. http://arks.princeton.edu/ark:/88435/k930bx11x

It turns out several were removed from the album some years ago (or were already loose) and were matted separately.

This dark, rich photogram was at the top of p. 45 in the Willats album, clearly indicated by the trimmed corners. A note on the page says “Energiatype by John Croucher” but this is not an iron-based print and the note must refer to the missing photograph at the bottom right. The photographer of this photogram remains unknown.