Might be the same as http://mushroomobserver.org/32384. And also this observation: http://mushroomobserver.org/32770. On an old rotten Russula or Lactarius, cap 16 cm in diameter. I brought it home, but it won't last long. Update Cut one on half. It was rock hard and difficult to cut. Looked at part of it under the scope; no spores. It might be a sclerotium for a mycoparasite, something similar to Collybia tuberosa or C. cookei. Planted the remains, gills down, in my backyard. Hoping that something will fruit from the sclerotium. Update - July 2012 Two winters have past by and no sign of a fruitbody where these sclerotia were planted. Looks like this experiment failed to fruit.