Russia 1831 St. Petersburg to France Disinfected Nimmersatt Memel Stampless FL

Stampless folded letter, datelined St. Petersburg, to Calais, France, prepaid 1-1/2k from St. Petersburg to Memel, 86l from Memel to Forbach, with neatly-struck “KONIGL.PR.CONTUMAZ DIREKTION ZU NIMMERSATT” large type in black on reverse, further disinfection slits and rastel spike holes, further struck “P. MEMEL / 20 JULI”, oval “4 / AED” and boxed “PRUSSE / PAR / FORBACH”, red “fr” manuscript notation at foot, scarce.