Yes that is a good site (there's also a great Mycena site out there which I can't remember off hand but should be easy to find via google). Unfortunately the Coprinus genus has been radically changed into four separate genera (Coprinus, Coprinellus, Coprinopsis and Parasola) and the only species which remains in Coprinus is C. comatus, the
Shaggy Ink Cap. I wasn't aware of this fact until yesterday. The species names remain the same though so the site is still useful for keying out what kind of ink cap you've got, whatever its latest name is. The mushrooms don't care what they're called!