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ther,
so that the faces of the octahedron now predominate, and the sign, of
the same two elements but in reverse order, is O . <x>0°o. In
fig. 18 the cube has its edges replaced
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by the faces of the rhombic-dodecahedron, the sign being  while in fig. 19 there is the same combination, but with the faces of the cube subordinate, and hence the symbol is  The former figure, it will be
seen, has more the general aspect of the cube; the latter of the dodecahedron.
In
combinations of semitesseral forms with oblique faces, the tetahedron,
the rhombic-dodecahedron, or even the hexahedron, seldomer a
trigonal-dodecahedron, are the more
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common predominant forms. In fig. 20 two tetrahedrons in opposite positions, are combined. In fig. 21a
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