Hi, Anthony! Yes, of course ANTONIUS is the classical form of ANTHONY. With DAVID it is a litte bit more complicated: It is not a classical name used by the Romans. In the Latin bible DAVID is just DAVID. But in Germany there was a fashion of educated people to latinize their German names, sometimes by translating them literally into Latin. So there (16th / 17th century) you will find DAVIDUS next to Rudolphus or Henricus.