A Riker mount is a flat container used for mounting a specimen (typically plant or insect) on cotton wool or other backing material, often with transparent glass or plastic cover as protection. It was patented by Clarence B. Riker (d. 1947), American naturalist and drug manufacturer, in 1902.
References Merriam-Webster Dictionary New York Times, January 3, 1947 US Patent Office: US-0696750-A