Vintage German snail shell beads

These vintage glass beads were made in Germany in the 1960s. They are unique because they are different on the front and back. The front is the whorl pattern of the shell and the back is indented as if the shell were open in the back as a shell is. The bead is 17 mm from hole to hole and 11 across. It is 10 mm thick. The bead channel will accommodate up to a 0.5 mm cord. The color is a blue that is unique to the 1960s time period. The bead is translucent. There are about 12 beads on each strand.