Northboro MA
Page 2

These LBMs looked interesting to me.  They had a distinctive bun like umbo.  It looks like the slugs found them interesting too.
Darvin DeShazer thinks this might be Gymnopus dryophila.  George Riner agrees and points out that another name is Collybia dryophila.

They deposited a white print on the relative below them.  Hollow stem.