Vintage Super Powers Superman on 3rd series (33-back) offerless cardback. This was only released in Australia, which makes it one of the harder to find “US” cardbacks ever released. There is a crack in the outer bubble (there is an outer bubble and inner bubble on this variation) as shown in the top of the bubble in the pics. These usually sell higher, but the crack in the bubble is reflected in the price.
More info on this variation visit the Wiki page: http://www.superpowerswiki.com/collector-blog-on-33-back-cardbacks/