We review the taxonomy of the Madagascar endemic buthid genus Grosphus Simon, 1880. We split the genus and describe Teruelius gen. n. on the basis of nine morphological characters, six of them new for Grosphus: positions of trichobothria d2 on pedipalp femur and Eb3 on chela manus, number of pectine teeth, shape of female basal pectinal tooth, form of hemispermatophore capsule posterior lobe, spiracle shape, metasoma I ventromedian carination, telotarsal setation and UV fluorescence. We discuss functional and taxonomic aspects of these characters, and propose that Teruelius gen. n. is monophyletic, while Grosphus (sensu stricto) is paraphyletic. Some characters of Teruelius gen. n. suggest adaptations to xeric environments, some of Grosphus to humid environments. Neogrosphus Lourenço, 1995 shares characters with both Grosphus and Teruelius gen. n. Scenarios for origins of these genera by vicariance or dispersal are discussed. New synonymies proposed are: Grosphus simoni Lourenço, Goodman & Ramilijaona, 2004 = Grosphus madagascariensis (Gervais, 1843), syn. n.; Grosphus halleuxi Lourenço, Wilmé, Soarimalala & Waeber, 2017 = Grosphus madagascariensis (Gervais, 1843), syn. n.; Grosphus mandena Lourenço, 2005 = Grosphus madagascariensis (Gervais, 1843), syn. n.; Grosphus hirtus garciai Lourenço, 2001 = Grosphus hirtus Kraepelin, 1900, syn. n.; Grosphus makay Lourenço & Wilmé, 2015 = Teruelius feti (Lourenço, 1996) comb. n., syn.n.; Grosphus rossii Lourenço, 2013 = Teruelius mahafaliensis (Lourenço, Goodman & Ramilijaona, 2004) comb. n., syn. n.