Anytime you use the effect of a card to summon a monster to the field, its a Special Summon.
Pay 800 points to negate Special Summons....
Just chain to the activation of The Ritual Spell Card to negate and destroy it.
AND, any summon outside of a Normal Summon, "Flip Summon" (flip summons are not considered normal summons, as you can do more than one per turn), and Tribute Summon (tribute summon is still considered a normal summon, as again, you can only perform one per turn) is considered to be a Special Summon. Just adding to what Digital Jedi stated.