Citation: Wyckoff, R. W. G. (1931). Page 292 from the second edition of Structure of Crystals by Wyckoff R W G. Published by The Chemical Catalog Company, INC, New York in 1931 & http://jcrystal.com/steffenweber/gallery/StructureTypes/st4.html. The second edition of Structure of Crystals, , pp. 292-292.