# Bipyramid

The "n-gonal" in the name of a bipyramid does not refer to a face but to the internal polygon base, lying in the mirror plane that connects the two pyramid halves. (If it were a face, then each of its edges would connect three faces instead of two.)

thus not all its faces are congruent (its upper faces are congruent scalene triangles, and its lower faces are congruent isosceles triangles).