 It has been considered a partially albinistic population of the François' langur ("T. francoisi"), a subspecies of Francois' langur, a valid species ("T. leucocephalus"), or a subspecies, "T. poliocephalus leucocephalus".Comparably, "poliocephalus" was considered a subspecies of Francois' langur until 1995.Cat Ba island is the largest island within the Cat Ba archipelago, with 366 smaller islands and tidally exposed rocks surrounding it.