This format was differentiated by the introduction of the cover artwork by Thelma Gooch.  A drastic improvement over the previous artwork, in my opinion--although still confusing as to why only one set of twins was shown. 

Any blank spots below are copies that I do not have in my collection--they may exist in this format though.  I don't know what the last title to be printed in this format is yet. 

Any pictures below that are not 'flat scans' were grabbed from the internet--basically eBay. 

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