This is the last in a series of papers clarifying the taxonomy of a critically imperiled assemblage of cochliopid gastropods (Tryonia sensu lato) that inhibit thermal springs in the Chihuahuan Desert (Mexico and United States). We describe 2 new narrowly endemic species of Tryonia from Chihuahua, both of which appear to have been recently extirpated, and we provide new records for 4 congeners (also from Chihuahua) and for a species of Pseudotryonia (from Durango). The 2 new species of Tryonia differ from closely similar regional congeners in shell and penial characters. On the basis of new anatomical data, we also transfer T. brunei Taylor, 1987 to the genus Juturnia and provide evidence that this species, which was endemic to the Phantom Lake spring complex in west Texas, became extinct sometime after 1984. Our findings provide additional insight into the complex biogeographic history of the Chihuahuan Desert cochliopids and further document the recent decline of regional spring-dwelling biota as a result of groundwater mining.