1. At present it is certain that Typhlomolge rathbuni inhabits the subterranean water of the Purgatory Creek System just north of the Balcones scarp line and one mile further up, and the caves of the Artesian Well of the U.S. Fish Hatchery at San Marcos, which seem to be in direct communication with the Purgatory Creek System by means of channels about 200 feet deep. 2. The populations of the species Typhlomolge rathbuni north and south of the present Balcones scarp line have not been separated from each other by the process of faulting in Eocene time, but have developed in unrestricted communication with one another. 3. No certain data are available as regards the occurrence of Typhlomolge in the San Marcos Springs and in the dry valley of the San Marcos River north of the Springs. Since the Springs come from the same water reservoir as the Artesian Well, further investigations should be conducted. 4. All the localities containing Typhlomolge are located in the Edwards limestone region, but the caves of the Artesian Well are 200 feet deeper than the rest. 5. Typhlomolge have been found in the Purgatory Creek System at an elevation of approximately 585 feet above sea level. Where this level could not be reached as in the upper Purgatory Creek valley, only remnants of the Purgatory Creek System fauna (Stygonectes flagellatum) were found. 6. The water inhabited by Typhlomolge seems to be slowly flowing water. 7. The temperature of the water is approximately 21.5° C and it is inhabited by the decapod Palæmonetes antrorum. Since the latter animal is much more numerous and can be detected much easier than the Typhlomolge, its presence may be taken as an indication that the place is promising as regards the presence of Typhlomolge. 8. The rarity of the Typhlomolge seems to be due to the animal's habit of preferring deep lying cracks or crevices, completely filled with water at a higher pressure than exists in the more open bodies of water located at higher levels. 9. As regards the habits of the Typhlomolge in its natural habitat we were able to confirm Normann's observations made in the laboratory in respect to the peculiar mode of walking of this animal and its indifferent attitude to light. But we did not find the animal particularly sensitive to water waves. 10. In feeding and swimming when aroused, Typhlomolge shows a close resemblance to larvæ of Eurycea rubra. 11. The assumption, however, that Typhlomolge is the larva of some unknown and still existing species of the genus Eurycea as made by Emmerson could not be confirmed, since with the exception of the species Plethodon glutinosus no tailed Batrachians were found in the caves. More important than this assumption is the fact that Typhlomolge, according to Emmerson, lack a thyroid, which would explain why these animals cannot metamorphose. 12. In order to collect a large number of specimens necessary for experimental work and intensive study of the species, as many places as possible must be discovered which may contain Typhlmolge, and collecting must be conducted simultaneously in all these places. 13. The best method of catching the animals is by trapping, but this method must be improved. It seems probable that live bait is not attractive to the animals. Instead of relying upon bait, the large openings of the traps should be laid in the path of the animals.