While working at the Maryland Academy of Sciences this past winter I found the specimen that forms the basis for the present article. It was collected a number of years ago from the Choptank formation a little north of Jones Wharf, St. Mary's County, Maryland, by John Widgeon, and represents a large blister pearl attached to the shell of Panopea americana. Before taking up the question of fossil pearls it is well to review briefly the different types of recent pearls and how they are formed. After which I will discuss the blister pearl in question.