What does "galleass" mean?

Galleass: A large galley, having some features of the galleon, as broadside guns; esp., such a vessel used by the southern nations of Europe in the 16th and 17th centuries. See Galleon, and Galley. [Written variously galeas, gallias, etc.] Note: "The galleasses . . . were a third larger than the ordinary galley, and rowed each by three hundred galley slaves. They consisted of an enormous towering structure at the stern, a castellated structure almost equally massive in front, with seats for the rowers amidships." Motley.