Official entire letter written "την 21 Μαίου 1858/Σέριφος", oval cachet on text ΝΟΜΑΡΧΙΑ ΚΥΚΛΑΔΩΝ..." to Syros. Linear "ΣΥΣΤΗΜΕΝΟΝ" in red (registered), arr. "ΣΥΡΟΣ*22.ΜΑΙΟΣ.58" (Type III). Cachet "ΥΓ.ΣΤΑΘΜΟΣ ΣΕΡΙΦΟΥ" on flap and on text side. Very fine and rare.