Greetings donatelli and welcome aboard,
Your gun is what's commonly known as "hardware store" or "brand name" gun. There was a time when gun manufactures would custom label their guns for individual stores, or chains. A little Googling tells me your "Delphian" seems to be made by Crescent Firearms (or its successor, Stevens) for the Supplee Biddle Hardware Co. of Philadelphia, PA. Delphian Arms Co. and Delphian Manufacturing Co. are just two of the well over 100 brands used by Crescent's customers. There is no correlation readily available for serial number and date of manufacture; but, a deep search may turn one up. Good luck.
