Well, Dr. Bill, you see, it's really quite simple...there is the eponym and then there is the eponymes (e-po-neye-mees). The first is a singular name derivative, and the second is a group name derivative. Eponymes was once the God of Orgiastic Splendor among the Lexiconites (an ancient Latin/Greek mixed sect in what is now Macedonia), thus the group connotation.

And Cybele is Diana (and vice versa...YCLIU).