I'm not exactly certain what this is called or what the precise purpose is, but
it is an assembly of extra shingles which are attached to the hatch via a hinge
and "float" over the shingles of the crew and equipment section's exterior. The
extra shingles appear to be attached to the exterior of the crew and equipment
section as well as attached to the hatch, and appear to slide on pins. Gemini
8 is rotated so that the pilot's hatch is
higher off the ground, so it was more difficult to photograph than, say, Gemini 12.
Unlike Gemini 12,
Gemini 8 does not have these shingles on the other side of the spacecraft. Unfortunately, I
did not think to inspect that side for any associated hardware.
Picture 1 of 6.
If you look carefully under the shingles at the edge closest to the camera, you
can see one of the pins attaching the shingles to the spacecraft, similar to
this picture of Gemini