User blog comment:Percy Jackson12/The Seven/@comment-4525239-20111015093403/@comment-3146930-20111015144100

But unlike Ma Gasket who is a Roman monster, Phineas is a mortal. He existed (going by mythology) during the time of Jason and the Argonauts. If he died, he would have spent his time in the Underworld during the Roman empire meaning he would know the Roman names from the new arrivals. Just because he used the Roman names doesnt mean he must be Roman. But lets say you are right and the book says that Phineas is in fact a son of Neptune, then the Son of Neptune has a grand total of 1 son of Neptune.