More species of nocturnal primates are now recognized than in the past, because many are cryptic species. Subtle morphological disparities, such as pelage pattern and color variation, vocal cues, and genetics have aided in elucidating the number of diagnosable species in a genus. The slow lorises (genus Nycticebus) once included only two species, but recent taxonomic studies resulted in the description of three additional species; further incompletely explored variability characterizes each of the currently described species. The Bornean loris in particular is characterized by pelage and body size variation. In this study, we explored facemask variation in the Bornean loris (N. menagensis). Differing facemask patterns, particularly influenced by the amount of white on the face, significantly clustered together by geographic regions, separated by notable geographic boundaries. Our results support the recognition of four species of Bornean lorises: N. menagensis, N. bancanus, N. borneanus, and N. kayan. Genetic studies are required to support these findings and to refine further our understanding of the marked variability within the Bornean loris populations. Key words: Nycticebus menagensis; Nycticebus bancanus; Nycticebus borneanus; cryptic species; morphology; sympatric, allopatric photo: http://www.nocturama.org/little-firefaces-2/borneos-new-lorises/ photo: http://www.nocturama.org/little-firefaces-2/borneos-new-lorises/ Taxonomy of the Lorises Nycticebus of Borneo Nycticebus kayan Munds, Ford, Nekaris 2013 photo: http://wildborneo.com.my/thumbs.php?k=primate Type locality: Peleben, East Kalimantan, Borneo, Indonesia Etymology: The specific name kayan comes from the Kayan River, which flows through the range of the species, close to the type locality of Peleben. Distribution: Nycticebus kayan is located in central and northern Borneo (Sarawak, Sabah, and East Kalimantan). Its southern range extends to the Mahakam River in East Kalimantan and the Rajang River in Sarawak. It is found as far north as the base of the southern part of Mt. Kinabalu in Sabah. It spans the width of Borneo, east to west, but unlike its neighbor (N. menagensis), it appears not to be found along the coast. It is sympatric with N. menagensis in East Kalimantan and Sabah. Three new species of venomous primate identified; May help protect rare primate from illegal trades: http://www.sciencedaily.com/releases/2012/12/121213172310.htm http://phys.org/news/2012-12-species-borneo-enigmatic-primate-toxic.html via @physorg_com R. Munds, S. Ford, K.A.I. Nekaris. 2013. Taxonomy of the Bornean Slow Loris, with New Species Nycticebus kayan (Primates: Lorisidae). American Journal of Primatology. 75 (1); 46-56 DOI: http://dx.doi.org/10.1002/ajp.22071 http://www.nocturama.org/wp-content/uploads/2012/12/2013MundsetalBorneanLorisTaxonomy.pdf