Delta the dog of (Pompeii or) Herculaneum

Can anyone help with this query we have received from a researcher in the USA. We have found a reference to it in a book of 1822 but there is no source information quoted to prove this as myth or fact. There are references to the dog being found in Herculaneum and the the collar, with a Greek inscription, being (then) in the Gallery of the Grand Duke of Tuscany. (Other versions elsewhere refer simply to the excavations at Pompeii and Herculaneum).

The query is

"I stumbled upon a story that might be urban myth, even though it's all over the Internet. I can't seem to find documentation for the story about this heroic dog.

It's not about the dog that was chained up. It's about the dog who was protecting a child that day in 79 AD. I read that a dogs skeleton was found laying over the body of a child about the age of ten or twelve. The dog had a silver collar that was engraved with his name "Delta" and it also recounted how he had saved his master, Severinus (Severino) from death on three occasions. Some accounts say the child was Severinus, and some say he was the son of Severinus."

Can anyone help prove it myth or fact?

Jackie and Bob at pompeiiinpictures