| Set of cupolae | |
|---|---|
 Example: pentagonal orthobirotunda | |
| Faces | 2n-gons 2npentagons 4ntriangles |
| Edges | 12n |
| Vertices | 6n |
| 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 |
| Properties | convex |
Ingeometry, abirotunda is any member of a family ofdihedral-symmetricpolyhedra, formed from tworotunda adjoined through the largest face. They are similar to abicupola but instead of alternating squares and triangles, it alternatespentagons and triangles around an axis. There are two forms,ortho- andgyro-: anorthobirotunda has one of the two rotundas is placed as themirror reflection of the other, while in agyrobirotunda one rotunda is twisted relative to the other.
The pentagonal birotundas can be formed with regular faces, one aJohnson solid, the other asemiregular polyhedron:
Other forms can be generated withdihedral symmetry and distorted equilateral pentagons.
