Definition of "membranaceous"

"Nay he confirms what his Antagonist has wrote, partly by History, and partly by Reason; affirming that himself in his own Garden found two little birds with membranaceous wings utterly devoid of Legs, their form was near to that of a Bat's."

1662, Henry More, An Antidote Against Atheism, Book II, A Collection of Several Philosophical Writings of Dr. Henry More, p. 75