PLATE A. 
Figs. 1—26.—Planes of Crystals and Separate Crystalline Forms. 
1. Square, ov face of a cube ; an equilateral rectangular parallelogram. 
2. Cube, or square prism, contained in six equal square sides. 
3. Rhombus, an equilateral oblique-angled parallelogram. 
4. Rhombic dodecahedron, or granatoid, bounded by twelve equal rhombic planes. 
5. Rectangle, an unequal-sided parallelogram, having a right angle. 
6. Rectangular prism, or right rectangular prism, bounded by six rectangles, whereof every opposite two are equal. 
7. Rhomboid, an unequal-sided oblique-angled parallelogram. 
8. Oblique rhomboidal prism, contained in six rhomboids, of which every opposite two are equal. 
9. Trapezium, unequal-angled quadrilateral with two parallel sides. 
10. Icositetrahedron, bounded by twenty-four trapezium-like planes. 
1 ]. Trapezoid or deltoid, a quadrilateral with two pairs of equal sides. 
12. Trapezoid or deltoid four-and-twenty-faced-solid, or leucitoid, contained in twenty-four equal trapezoidal planes. 
13. Equilateral or regular triangle. 
14. Regular octahedron , enclosed in eight equal equilateral triangles. 
15. Isoceles triangles, with two equal sides. 
16. Quadratic octahedron, or tetragonal octagon, contained in equal isoceles triangles. 
17. Scalene , or unequal-sided triangle. 
18. Rhombic octahedron, contained in eight equal scalene triangles. 
19. Pentagon, bounded by five sides, of which one is larger than the other. 
20. Pentagonal dodecahedron, surrounded by twelve equal pentagons. 
21. Hexagon, regular, contained in six equal sides, which cut each other at equal angles. 
22. Hexagonal prism, regular, with two regular hexagonal basal planes, and six equal, rectangular lateral planes. 
23. Symmetrical octagon, with alternate equal sides and equal angles. 
24. Octagonal prism, the terminal planes, as in Fig. 23 ; the lateral planes being right angles. 
25. Dodecagon. 
26. Dodecagonal prism. 
