Patera versus Phiale
According to wikipedia, a patera was a broad, shallow dish used for drinking, primarily in a ritual context such as a libation (a ritual pouring of a drink). According to NumisWiki, a phiale was a flat Greek drinking cup (libation bowl). In researching another topic, I found the following discussion on forumancientcoins about a dot in a patera. According to Pat (slokind) the dot symbolizes that it is a "phiale mesomphalos. Like a patera, it is used for pouring a libation, but it has a lump in the center--because it has a hollow for one's longest finger to help you to hold it steady while it is full of wine, or even when it is half full; a flat dish full of liquid can be hard to control. Whenever you see the dot in its center, the vessel is the Greek phiale rather than the Roman patera." Pat also pointed out this website with a picture of a phiale mesomphalos. As these coins depict Greek gods, rather than Roman ones, you might think that the phiale would be more common than the patera, however I find that most references are to the patera. Some references seem to use the two words interchangeably. In Varbanov, it references the phiale on coins of Cybele, Hera and Zeus though Hera and Zeus are also listed as using a patera on other coins. I have 2 coins Homonoia that definitely show a phiale rather than a patera as well as one of Hera.
Three examples of the phiale:
Homonoia or Harmonia (Concordia) standing facing, head right, holding phiale left over lighted altar and cornucopia.
Homonoia standing left holding phiale and cornucopia wearing kalathos.
Hera (Juno) standing left holding phiale and sceptre.