heptagonal

It is a little heptagonal recess, paved with white marble and roofed with a shell-like cupola of marble of a single block.

Meshes regular or subregular, hexagonal, often intermingled with a variable number of pentagonal and heptagonal meshes.

Meshes subregular pentagonal (intermingled with single tetragonal, hexagonal, and heptagonal meshes).

Shell-mantle one and a third times as long as broad, its frontal perimeter heptagonal, with seven concave sides.

The effect of a heptagonal stem on an octagonal base or plinth is certainly odd.