The best way I've found to identify the little babies you are after is the 'blue test' . When the mushroom is picked it should bruise a shade of purple/blue around the stem, give the cap a pinch and quite quickly it should also get a blue tinge, my understanding is that this indicates the presence of psilosybin.
I won't take a mushroom that dosn't turn blue in some way and have always had great success with this method,
Antbody else?