There are 5 books in the A Natural History of Dragons series. The newest book is Within the Sanctuary of Wings which came out in 2017.

Everyone knows Isabella, Lady Trent, to be the world's preeminent dragon naturalist. Here at last, in her own words, is the true story of a pioneering spirit who risked her reputation, prospects, and her life to satisfy scientific curiosity; of how she sought true love despite her lamentable eccentricities; and…
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2
The Tropic of Serpents

Book cover of The Tropic of Serpents
Three years after her fateful journeys through Vystrana, the widowed Mrs. Camherst defies convention to embark on an expedition to the savage, war-torn continent of Eriga, home of the legendary swamp-wyrms of the tropics. Accompanied by an old associate and a runaway heiress, Isabella must brave heat, fevers and palace…

3
Voyage of the Basilisk

Book cover of Voyage of the Basilisk
"Wonders terrestrial and aquatic, ancient ruins, near drownings, and more kinds of dragon than you can shake a wing at..." > > Six years after her perilous exploits in Eriga, Lady Trent embarks on her most ambitious expedition yet: a two-year trip around the world aboard the Royal Survey Ship…

4
In the Labyrinth of Drakes

Book cover of In the Labyrinth of Drakes
Lady Trent's discoveries in Akhia are the stuff of romantic legend, catapulting her from scholarly obscurity to worldwide fame. The details of her personal life during that time are hardly less private, having provided fodder for gossips in several countries. But, as is so often the case in the career…

5
Within the Sanctuary of Wings

Book cover of Within the Sanctuary of Wings
After her adventure in the mountains of Vystrana, and her exploits in the depths of Eriga, to the high seas aboard The Basilisk, and then to the deserts of Akhia, the Lady Trent has captivated hearts along with fierce minds. This concluding volume will finally reveal the truths behind her…