EXPLANATION OF THE PLATES* Fundamental Figures. tlG. 1. The Icosahedron. 2. The Dodecahedron. The Hexahedron, as 3. Cube. 4. Rhomb. 5. Rectangular-tetrahedral prism. 6. Oblique-angular tetrahedral prism. 7. Oblique-angular tetrahedral prism, in Which the terminal planes are set obliquely on the lateral planes. 8. Equiangular-hexahedral prism. 0. Tetrahedron, or simple three-sided pyramid. 10. Double three-sided pyramid, in which the lateral planes of the one pyramid are set on the lateral edges of the other. 11. Octahedron. 12. Simple six-sided pyramid. 13. Double six-sided pyiamid, in which the lateral planes of the one pyramid are set on the la teral planes of the other. 14. Double six-sided pyramid, in which the planes of the one pyramid are set obliquely on those of