Circa 1972. Cover franked with pair 1972 75p apple green (SG 1521) tied by boxed 'O.N.D.A. S.A AGENCIA No. 76 CASTILLOS' cancel of Organización Nacional de Autobuses. Addressed to MONTEVIDEO with black on yellow 'ONDA S.A. CASTILLOS MONTEVIDEO 1o R' label attached on reverse.