Extragene Petri Dishes, 150 x 15mm, beveled stacking rings, Sterile, Clear, Pk x 10 Optical clear polystyrene with consistently flat bottoms. Designed for easy one hand opening and closing. Edges of tops and bottoms are squared off to provide a firm sure grip. Dishes have four to six venting ribs on the underside of the lid. To prevent condensation build up. Gamma ray steriled.