Octadecadiminished pentacontatetrapeton

The bitriangular trioprism, also known as the octadecadiminished pentacontatetrapeton or oddimo, is a convex scaliform polypeton that consists of 18 triangular duoantiwedges and 54 digonal-triangular duoantiwedges formed from deleting the vertices of a hexagonal triotegum from a pentacontatetrapeton. It is the second member of the bitrioprisms formed from the convex hull of two rotated trioprisms and the only convex scaliform one.

It is also the convex hull of a triangular trioprism and its central inversion.

Vertex coordinates
The vertices of a bitriangular trioprism of edge length 1 are given by:
 * ±(0, $\sqrt{3}$/3, 0, $\sqrt{3}$/3, 0, $\sqrt{3}$/3),
 * ±(0, $\sqrt{3}$/3, 0, $\sqrt{3}$/3, ±1/2, –$\sqrt{3}$/6),
 * ±(0, $\sqrt{3}$/3, ±1/2, –$\sqrt{3}$/6, 0, $\sqrt{3}$/3),
 * ±(0, $\sqrt{3}$/3, ±1/2, –$\sqrt{3}$/6, ±1/2, –$\sqrt{3}$/6),
 * ±(±1/2, –$\sqrt{3}$/6, 0, $\sqrt{3}$/3, 0, $\sqrt{3}$/3),
 * ±(±1/2, –$\sqrt{3}$/6, 0, $\sqrt{3}$/3, ±1/2, –$\sqrt{3}$/6),
 * ±(±1/2, –$\sqrt{3}$/6, ±1/2, –$\sqrt{3}$/6, 0, $\sqrt{3}$/3),
 * ±(±1/2, –$\sqrt{3}$/6, ±1/2, –$\sqrt{3}$/6, ±1/2, –$\sqrt{3}$/6).

These coordinates show that a bitriangular trioprism can be obtained as the convex hull of two inversely oriented triangular trioprisms.