The Bay Area Mycological Association has a great website that identifies the most deadly mushrooms and shows many photos. There is variability of cap color, size and ornamentation in Amanita phalloides, the Death Cap Mushroom. Please take heed and look at the pictures carefully.
http://www.bayareamushrooms.org/poisonings/index.html
http://www.bayareamushrooms.org/mushroommonth/amanita_phalloides.html
The North American Mycological Association has a very good page about mushroom poisonings in dogs and cats.
http://namyco.org/toxicology/pet_poisonings.html
Here's two more good pages that describe DeathCaps and how to identify them.
http://www.mushroom-appreciation.com/death-cap.html
http://www.mushroom-appreciation.com/identify-poisonous-mushrooms.html
