One of the Stranger & More Enigmatic of Clarks works on Thurian-Related lands and events, PTOLEMIDES is unclear as to where it has fallen in the timeline or even it's location.
Never finished, its inclusion in The Thurian Cycle comes after much research and some speculation has led me to believe this story is from Thurian Age Stygia and One of it's own Coastal Islands, doomed to be Destroyed in the coming Cataclysm that rocks the world.
Based on what information we have, POSEIDONIS & LEMURIA Cover much of this series, with PTOLEMIDES being the only story set within this strange land.
Some may not like that this will inevitably serve as the end of The Thurian Cycle, but keep in mind, Real History is filled with gaps in the greatest of tales. Look to the many volumes of Titus Livius missing from The History of Rome.
Consider than, that the Libraries of the world rocked by the cataclysm turned to vapor, rubble and were drowned or turned to dust. It's a miracle any of this survives to the modern Era.