The snap ring is about the diameter of a coat hanger and goes in a groove in the base to hold in the lense. The dental hook goes at the end of the snap ring and carefully pull it towards the center and hold on to the lense, because it is milk colored glass. The base you refer to is attached behind the lense by wood screws into the top bow support for the light. You do need to pry on that base.
Hope that helps.