Gibraltar SG115b 1935 Silver Jubilee 3d Short Extra Flagstaff on Cover

1936 (4 May) envelope air mail registered to USA bearing full set-in blocks of four the lower left stamp of the 3d. block showing variety short extra flagstaff each cancelled by oval registered datestamp a most appealing cover. S.G. 115b (375 pounds as a used stamp). Grosvenor