This "D" shaped head looks right (towards the south).   I am struck by its unusually prominent ear which juts out towards the camera, and also by its remarkable rear sloping skullcap.   These remind me forcibly of similar features visible on the impressive Stone 21 head inside West Kennet Long Barrow.   I therefore wonder if our Avenue Stone 24b references that stone in the far older Barrow, a fundamentally important primeval artwork celebrating rebirth?*

While there doesn't appear to be a carved eye socket or eye panel here on 24b, it is clear that this is stone is definitely intended to be a head in profile because of the addition of a hacked out mouth, visible at the lower right.   This kind of minimalist carving (which elevates a simulacrum into a sculpture) is very typical of the Avebury artistic style.

*For a discussion of the significance of WKLB Stone 21 and its theme of resurrection see Meaden, "Secrets" book p104, and for a particularly clear photograph showing that stone's distinctive ear and sloping crown see Marshall "Exploring Avebury" p52.