The members of the Cortinarius genus of mushrooms, once thought to be harmless, are deadly poison—almost as poisonous as the Amanita genus of mushrooms. A little more than a cup of the cooked mushrooms can be fatal. Found in central Europe, the mushrooms have caps ranging from blue violet (which can be eaten) to those of brown or red (deadly); they get their name from the veil that sometimes covers the gills of young mushrooms.

Ref: The Encyclopedia of Poisons and Antidotes (Turkington-Mitchell)