United States. (Porto Rico). 1917. Registered envelope headed 'Consulate de Belgique a/ Saint Jean de Porto Rico' addressed to France bearing United States Yvert 90, 15c grey tied by 'San Juan/ P.R. oval with boxed hand-struck 'Registered/ No' in violet and circular 'San Juan P.R./ Registered' date stamp on reverse , routed via Spain with framed 'Certificado/ Madrid' and oval censor 'Controle Militaire/ Achemine sans Controle/ 400' in violet applied in transit in Bordeaux with La Havre receiver. Very fine and scarce.