I went to the University library this afternoon and dug out an *ancient* copy of Baird's Manual and found some information about Phi Delta Gamma. It was founded at the University of Maryland in 1923 as an organization for women graduate students, but by the looks of it, the organization is now co-ed. They don't seem to have a national website, but the chapter at CSULB has a page here:
http://www.csulb.edu/aux/alumni/chapters/phideltagamma/