Purrified Air Discount Group B consists of our award winning litter box air filter, a second sealed filter media cartridge, and adapter for a domed-shaped litter box and a wall-mount, table-top bracket. Be sure to specify whether you need the Model AC (for smaller dome-shaped litter boxes with the cutout, or the Model AR for larger dome-shaped -- the type with steps -- litter boxes. Total savings: $29.99. Plus free shipping in United States. $15 off shipping to Canada.