It is a three-unit hexahedron built around the notional scaffold of a flat equilateral triangle ( two " faces ", three edges ); the protruding tab / pocket flaps are simply reconnected on the underside, resulting in two triangular pyramids joined at the base, a triangular bipyramid.
22.
The " hemi " part of the name means some of the faces form a group with half as many members as some regular polyhedron here, three square faces form a group with half as many faces as the regular hexahedron, better known as the cube hence " hemihexahedron ".
