Dragons of Daegonlot by Shanlynn Walker (best ereader for textbooks .txt) 📕

This is the beginning of the second book in the Dragons of Daegonlot series, titled Into the Myste.  The first book, Dragon Orb, introduced Daxon and Drakthira and set them on a journey to destroy the orb that they fear is holding dragons in thrall.  Along the way they meet Sylas, a dog borne of the Myste with the help of his companion, Trakon, who proclaims he is the first dragonrider.