I am going to call the rear marker light there......the pic is so low resolution that you cant enlarge it much without it getting pixelated. But I have seen on my own 68 that at certain angles and at a distance the rear marker gets absorbed by the rear bumper and looks absent when it is in fact there.
I would bet a better resolution photo would reveal the marker.....look at the photo in the link, not the one posted on this page
At least that is what I would bet on
