|Set of birotundas|
(Example Ortho/gyro pentagonal forms)
|Symmetry group||Ortho: Dnh, [n,2], (*n22), order 4n|
Gyro: Dnd, [2n,2+], (2*n), order 4n
|Rotation group||Dn, [n,2]+, (n22), order 2n|
In geometry, a birotunda is any member of a family of dihedral-symmetric polyhedra, formed from two rotunda adjoined through the largest face. They are similar to a bicupola but instead of alternating squares and triangles, it alternates pentagons and triangles around an axis. There are two forms, ortho- and gyro-: an orthobirotunda has one of the two rotundas is placed as the mirror reflection of the other, while in a gyrobirotunda one rotunda is twisted relative to the other.
Other forms can be generated with dihedral symmetry and distorted equilateral pentagons.