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Perhaps the most useful classifications of clusters of galaxies at the present time are those of (1) Abell (1958); (2) Zwicky, Herzog, and Wild (1961); and (3) the recent two-part division of Abell (1965, 1970). Each has its special criterion: richness, in (1); concentration, in (2); and the separation in (3) into clusters of two differing average stellar populations. A more detailed expansion of (3) is implicit in a discussion by Morgan (1962), which suggests a classification in which the Coma, Virgo, and Ursa Major clusters can be considered as type-objects for a morphology paralleling that of open star clusters in the Galaxy; its use, however, is limited to the nearer clusters, because of the necessity of determining form types for the brighter individual galaxies in each cluster. The importance of the Abell two-part classification is great, since it can be applied to clusters over great ranges in distance.