Ansley W. Sawyer wrote:
The ketch in the picture is sailing a genoa, main, mule, and mizzen.

"mule sail n. A staysail hung with the point down and carried between the
mainmast and the mizzen on ketches."

The Sailor's Illustrated Dictionary by Thompson Lenfestey published 1994 The
Lyons Press


Thanks for the reference.

The sail in the picture could be considered a main topsail,
it could also be called a Fenger staysail, after a yacht
designer of the early 1900s who produced boats with rigs
like this.
http://www.shipyardcup.com/boats-sintra.jpg
Of course, if you call it anything, most people won't know
what the heck you're talking about

Fresh Breezes- Doug King