Melicopine, melicopidine, and melicopicineare shown to be members of a new group of alkaloids derived from acridine. Thestructure of melicopicine, 1, 2, 3, 4-tetramethoxy-10-methylacridone (II), is deduced from data reported in earlier papers. The presence of the same10-methylacridone skeleton in melicopidine and melicopine is established by conversion of the trimethoxyphenols obtained from them by fission of themethylenedioxy ring with methanolic potash to the respective dimethoxy-o- and p-quinones previously prepared from melicopicine. This conversion alsoestablishes the position of the methylenedioxy group in melicopine relative tothe hydroxyl group in normelicopicine. Similar considerations applied to theethoxydimethoxyphenols show the position of the methylenedioxy group inmelicopidine relative to the hydroxyl group in normelicopicine, and in this case, lead to the complete structure for the alkaloid (XIII). © 1949 CSIRO. All rights reserved.