Sphaerolana, new genus, the second known American cirolanid isopod capable of flexing its body into a ball, is described from the Cuatro Cidnegas basin, central Coahuila, northern M dxico (type species, S. interstitialis). Two new species, S. interstitialis and S. affinis, both living in sediments of thermal springs, occur in partial sympatry in the area. Comparisons with the European genus Faucheria, and with the genus Creaseriella from Yucatan, Mdxico, indicate no close relationships. Most resemblances appear superficial, a result of parallel evolution. Ecology, associated crustacean species, and distribution of the two new forms are discussed. The northern part of the Mexican Plateau is yet poorly known from the biological standpoint, and the aquatic and mesic habitats of that vast, arid region continue to yield unique faunal elements. The Cuatro Cidnegas basin, because of its extensive series of aquatic environments (Minckley, 1969), supports a remarkably large and diversified biota, including a number of troglobitic crustaceans. One of these is 'an asellid o fthe subfamily Stenasellinae, the only known occurrence of that OldWorld group in the Western Hemisphere (Cole and Minckley, 1970). The other three forms are cirolanids, Speocirolana thermydronis Cole and Minckley (1966), and two well-marked species of the novel genus described below. Sphaerolana, new genus Unpigmented, eyeless. Capable of rolling into a ball. Pleonites 1-2 present, visible dorsally; no evidence of pleonites 3-5. Uropod sympodites broad, sub-triangular, narrow proximally; exopod and endopod greatly reduced, inserted in a notch on posterior margin of sympodite. Pereopods 1-3 prehensile, but pereopod 1 less so than the stouter 2-3. Exopods of pleopods 1-2, with plumose setae, all other rami unarmed; exopods of pleopods 4-5 partially divided by a suture.