In geometry, a rotunda is any member of a family of cyclic-symmetric polyhedra. They are similar to a cupola but, instead of alternating squares and triangles, they alternate pentagons and triangles around an axis. The pentagonal rotunda is a Johnson solid.
Other forms can be generated with dihedral symmetry and distorted equilateral pentagons.
Examples + Rotundas345678triangular rotundasquare rotundapentagonal rotundahexagonal rotundaheptagonal rotundaoctagonal rotunda
Star-rotunda + Star-rotundas57911Pentagrammic rotundaHeptagrammic rotundaEnneagrammic rotundaHendecagrammic rotunda
See also Birotunda
References Norman W. Johnson, "Convex Solids with Regular Faces", Canadian Journal of Mathematics, 18, 1966, pages 169–200. Contains the original enumeration of the 92 solids and the conjecture that there are no others. The first proof that there are only 92 Johnson solids.