Looks to me that the 1968 quarter has been ground down on about 2/3's of the coin. It doesn't look perfectly round anymore. The edge by the date looks good, but the rest of the edge has been worn away. Wait a sec.....on second look, it looks like you cropped the photo that cuts off some of the edge. In that case, it think it was just a quarter that got caught in a machine and was damaged that way. Definitely PMD.