TRINIDAD. 1935 underpaid envelope sent air mail from England with a 6d cancelled LONDON 10 DEC 1935. The cover has been taxed and a vertical strip of three 4d, a single 4d and a 2d Postage Dues have been affixed and cancelled SAN FERNANDO 28 DEC 35. The cost of an air mail cover was 1/3d and the underpayment was 9d, hence the 1/6d double deficiency tax. The 4d postage due is a very uncommon stamp on cover and this taxed franking is exceptional.