Vermax was a dragon ridden by Prince Jacaerys Velaryon during the reign of Viserys I Targaryen and the Dance of the Dragons.
In his Testimony, the jester Mushroom reports that Vermax left dragon eggs when Jacaerys Velaryon was in Winterfell in the year 129. If he reports this story, Archmaester Gyldayn finds it absurd.
While he admits that it is virtually impossible to determine the gender of a living dragon, he notes that no other historical source has ever claimed that Vermax laid an egg.
Gyldayn rejects the wild speculations of septon Barth, who claimed that dragons could change sex during their existence. The Archmaester concludes that we must assume that Mushroom's story is false and that we must assume that Vermax was a male.