This is an extremely early vintage Dolnet Paris tenor sax, serial number 10019. In fact it's the earliest Dolnet I've ever seen. It is stamped with the names of all of the partners in the original company: Dolnet, Lefevre, and Pigis. From keywork and build comparisons, I'd date this horn to the late 19th or very early 20th Century.
Henry Dolnet started his shop in Mantes, France (just west of Paris), which was the hub of music instrument manufacturing in France in the late 19th century. This example is silver plated (I believe it to be original) with moderate finish wear for its age. The sax features soldered on told holes, keywork from low Bb to high F, and has a couple unique features, including a very different-looking secondary octave mechanism. I believe this tenor was originally manufactured without pearl key touches, but they've been added here at some point for a more modern, and more comfortable, feel. Someone did replace pads at some point in this horn, but the sax is not playing as it sits.
This is definitely more of a conversation piece than a true player's horn at this point. It would be a neat addition to any collection, and a classic example of early French musical instrument production. Ships with original neck (which shows some past repairs, as seen in the photos) and in a hard case.