'Anthropologica Incognita comprises twenty classic short stories of wild men, monster apes, weird primates, and strange races. The works are: 'The Story of TsoqélEM,' 'Two Nights in Southern Mexico,' 'Hunting of the Soko,' 'Manmat'ha,' 'A Haunt of the Jinkarras,' 'From a Simian Point of View,' 'Dankwarra: the Isle of Fear,' 'The Depths of Kyamo,' 'No-Man's-Land,' 'The Harbour-Master,' 'Found by the Missing Link,' 'In the Lower Passage,' 'Beyond the Banyans,' 'Back There in the Grass,' 'The Ape-Man,' 'The Missing Link,' 'Facts Concerning the Late Arthur Jermyn and His Family,' 'Spirit Island,' 'The Horror-Horn,' and 'The Tale of the Abu Laheeb' (Amazon).
'A Haunt of Jinkarras deals with the discovery of a primordial race that dwells entirely underground.'
Source: L.W. Currey, Inc. https://www.lwcurrey.com/pages/books/167311/ernest-favenc/the-last-of-six-tales-of-the-austral-tropics