Image Number 3 for United States Patent #8163540.
A petri dish includes a cover and base, the cover having at least one circular opening in the top of the cover. A number of securing members are connected to the underside of the cover around the opening to secure at least one filter under the opening, the filter(s) being used to prevent any contaminants from the air from entering the petri dish. A guard member such as a plastic disc is disposed under the filter(s) to prevent any oil in the base of the petri dish from contaminating the filter(s). A sealing member is provided on a peripheral edge of the base to seal the petri dish when the petri dish is closed.