Abstract: Since the publication of the paper on the minerals of the montmorillonite group by Ross and Hendricks (1945) some species have been added to the group, and minor changes in the acceptable species have become advisable. No radical changes are proposed, but a review of the members and their grouping will be presented. The acceptable dioctahedral members of the group appear to be montmorfllonite, nontronite and volehonskoite. Beidellite should be discontinued. The acceptable trioctahedral members of the group appear to include saponite, hectorite, sauconlte, stevensite and medmontite. Griffithite is probably a useful term for an iron-rich saponite. Representative chemical analyses and formulas have been assembled to illustrate relationships.