| Set of cupolae | |
| Faces: | 2 -gons pentagons triangles |
| Symmetry: | Ortho: order Gyro: order |
| Rotation Group: | order |
| Properties: | convex |
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.
The pentagonal birotundas can be formed with regular faces, one a Johnson solid, the other a semiregular polyhedron:
Other forms can be generated with dihedral symmetry and distorted equilateral pentagons.