Meridian Library

It appears that these were titles published, unlike the exclusively paperbound Meridian Books, in both paperbound and cloth (i.e., library) formats. The earliest ad to mention them, at PW, Sept. 17, 1956, at 1225, lists ML1 - ML4 and has a note at the bottom that says "Note that ML1, ML2, ML3, ML4, and LA4 are available in hardcover library editions." There was evidently no piece announcing the publication of this line in PW, so it's difficult to verify what the stated reason for the line was. Some Meridian Library titles were later issued as Meridian Giants after World purchased Meridian.