Tepuis, the flat-topped mountains of northern South America have produced a fairly large endemic flora and fauna, including many endemic frogs but the discovery of endemic snakes have been far fewer. Now, Philippe J. R. Kok of the Unit of Ecology and Systematics, Vrije Universiteit Brussel, has described a new species of Chiroinus from Maringma Tepui, a flat-topped, sandstone mountain in the Pakaraima Mountains on the Guyana-Brazil border, the snake was found at 1500 m of elevation. Previous specimens of this snake had been collected between 1974 and 2004 but confused with C. fuscus. The new species, Chironius challenger is named after Arthur C. Doyle's fictional character Professor George Edward Challenger in the 1912 novel the The Lost World. It is known from four specimens collected from tepuis in Venezuela and Guyana. The holotype was found in the morning, active in a small tree about 200 cm above the ground in low evergreen upper-montane forest, another specimen had also been collected on the ground on the northeastern slope of Mount Wokomung, also in low evergreen upper-montane forest. Chironius challenger and C. fuscus are superficially similar, but C. challenger differs in having a higher number of ventrals, a lower number of subcaudals, a shorter tail) 9 infralabials instead of 10, an absence of apical pits, an absence of paravertebral keels in juvenile and females. Kok, P. J. R. 2010. A new species of Chironius Fitzinger, 1826 (Squamata: Colubridae) from the Pantepui region, northeastern South America. Zootaxa 2611:31-33.