Department circulars. 907. United States 2¾ percent treasury bonds, investment series B-1975-80, nontransferable, dated Apr. 1, 1951, with interest from Apr. 1 or Oct. 1, 1952, due Apr. 1, 1980, redeemable at option of United States at par and accrued interest on and after Apr. 1, 1975, interest payable Apr. 1 and Oct. 1, additional issue.