Seriously do not eat these without first ID'ing them.

The best way to ID this mushroom is with a good mycology book that catalogs multiple pictures of each specimen and also shows the gill print of the mushroom. Just like a finger print each mushroom has some highly definable charactaristics to it that set it apart from other mushrooms. One of the features used to determine which you are dealing with is to place the mushroom gill down on a piece of white paper until the spores have been liberally deposited on the paper. The spores are different colors and will dispurse differently depending on the mushroom. From there you should be able to ID along with size, color, gill or non-gill, stem, cap, etc. You can ID them but you need a really good field guide to do so. Even then with some species you are rolling the dice.

Best go to Safeway unless you can positively ID.