At the beginning of the second appendix in this three volume edition, vol. 3. p. 11 of the appendix, you have the abbreviation "Mm" explained as standing for the Mandāramarandacampū published in the Kāvyamālā series, No. 52, Bombay 1895. The definition of the meter Rājahaṃsī is on p. 9, line 11 of this edition. This is what Apte's abbreviation "Mm. 9.11" stands for.
On the next page, you have the illustration of Rājahaṃsī:
Madhav M. Deshpande
Professor Emeritus, Sanskrit and Linguistics
University of Michigan, Ann Arbor, Michigan, USA
Senior Fellow, Oxford Center for Hindu Studies
[Residence: Campbell, California, USA]