Wow, many thanks for that snippet.
I think the 1941 cutting I posted earlier suggests the circus stopped after his death.
Add
I wonder that that book has cited its sources ... if so, perhaps our OP would be interested in following those back to their primary origins. 
Cheers, JM
Yes the book has 3 pages of Sources
Newspapers, Magazines, Books, Playbills & Interviews.
"Interviews have been cited as appropriately throughout the book."
The St Leon family were circus performers not sure if they owned circuses.
In 1954 Leo St Leon was a fourth generation St Leon family performing under the Wirth canvas during the Sydney Easter season.
For interest Mark St Leon started preparing this book while in his final year at high school & completed the task 13 years later.