Miz Possum is the mother of the three Possums. She often refers to Fone Bone as "Uncle Bone" while the kids are around.
Out From Boneville
Eyes of the Storm
Miz' Possum shows up in the first chapter to talk with Fone Bone and Thorn.
Rock Jaw: Master of the Eastern Border
The possum kids reference their mother, saying, "But momma said to never go near the Eastern Mountains 'cause it might be dangerous..."