We introduce the Pentarkehedron (V=15, E=25, F=12, five triangles and seven pentagons, C5v symmetry) and its polar dual, the Umbrahedron (V=12, E=25, F=15, ten triangles and five quadrilaterals, C5v symmetry), as a new geometrically dual pair of convex polyhedra. Both solids are verified against twenty standard polyhedral families and confirmed new. The pair exhibits a self-referential duality: the face distribution of the Pentarkehedron equals the vertex-valence distribution of the Umbrahedron.
Jean Santillana (Sun,) studied this question.
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