Any educated person in the 19th century would know Greek and Roman mythology. Since ar least WW2, schools have dropped classical education.
Look in a "Classical Dictionary" such as Wordworths, by Wm. Smith, available in cheap paperback at most large bookshops. Most will be in this book. Some, like Susannah, I think are biblical. Words like deluces refer to noble family emblems of heraldry. I have the books (crossword nut), but I'm too lazy to look them up.

The song has so many references that I think it is a tongue-in-cheek composition meant to befuddle students. Quaegenus and candusus are not even in the complete Oxford Dictionary.
Deluce is the lily flower, ensign of the Bourbons.
I think some of our English classics scholars at Mudcat could help.