The Cat-eyed Snakes of Madagascar: Phylogeny and Description of a New Species of Madagascarophis (Serpentes: Lamprophiidae) from the Tsingy of Ankarana Sara Ruane 1,2 , Frank T. Burbrink 1 , Bernard Randriamahatantsoa 3 , and Christopher J. Raxworthy 1 The cat-eyed snakes of the genus Madagascarophis are among the most commonly encountered snake species in Madagascar. Yet despite their broad distribution and frequent occurrence in human-disturbed habitat, Madagascarophis still contains unrecognized species diversity. Here, we describe a new species of Malagasy cat-eyed snake from a specimen found in the tsingy karst system of Ankarana in northern Madagascar. Using multiple loci from all currently described species, including the never-before-sequenced M. ocellatus, we delimit a new species and also determine its placement within the genus in a Bayesian coalescent framework, using BPP and *BEAST, respectively. Our results indicate that molecular data are sufficient to delimit this new taxon. These data also support its placement as the sister taxon to the recently described M. fuchsi which is endemic to the Montagne des Fran¸ cais karst massif also in northern Madagascar. We also provide a morphological description of this new snake species, which can be readily diagnosed based on external morphological characters, and include a species identification key for the entire genus based on external morphology. W ITHIN the tropical regions of the world, the discovery of squamate species new to science is still common (amphisbaenids, Teixeira et al., 2014; snakes, Ramadhan et al., 2015; and lizards, Colli et al., 2015). In particular, the isolated island of Madagascar, with 100% endemicity of colubroid snakes, regularly yields species new to science (Vieites et al., 2010; Glaw et al., 2013a, 2013b). Among Malagasy snakes, the cat-eyed snakes of the genus Madagascarophis are among the most commonly encountered species throughout many habitat types. All species of Madagascarophis are crepuscular/nocturnal, both terrestrial and semi-arboreal (Glaw and Vences, 2007), and spend their daylight hours concealed, such as in the axils of bromeliads (Lehtinen, 2002). These snakes’ generalist diets include frogs, lizards, mammals, birds, and even other snakes (Bloxam et al., 1996; Andreone and Luiselli, 2000; Glaw and Vences, 2007). Species of Madagascarophis are distributed across much of the island (except at elevations above 1700 m) and within a variety of habitats, including, for example, taxa such as M. colubrinus regularly found in anthropogenically disturbed areas (Kaloloha et al., 2011). The close association of Madagascarophis with human-inhabited areas may be signif- icant from a medical standpoint; while not dangerously venomous, M. colubrinus is one of the few Malagasy species of opisthoglyphous snake known to cause envenomation and acute localized effects, which includes pain, swelling, blistering, and tissue necrosis (Domergue, 1989). Despite Madagascarophis being both common and of potential medical importance, new species of Malagasy cat-eyed snakes that are both genetically and morphologically distinct are still being discovered. Recently, Glaw et al. (2013a) described a possible microendemic restricted to Montagne des Fran¸ cais in northern Madagascar. This brings the number of species in the genus to a total of four: 1) the widespread M. colubrinus, 2) the southern/southwestern M. meridionalis, 3) the south- western M. ocellatus, and 4) the northern microendemic from Montagne des Fran¸ cais, M. fuchsi. Here we describe a new, possibly microendemic, species of Madagascarophis from the tsingy karst massif of Ankarana National Park in Antsiranana Province (Figs. 1–3). Ankarana is a limestone massif, with pinnacle-shaped karstic limestone formations (tsingy), narrow canyons, and massive under- ground cave networks. The natural vegetation is deciduous forest, which becomes more mesic in the bottom of canyons with water bodies. The surrounding habitat consists of relict deciduous forest and degraded grasslands with scrub. Many Malagasy reptiles are endemic to the northern region (Brown et al., 2016), with some known solely from Ankarana, including the rarely encountered snake Alluaudina mocquardi, the gecko Lygodactylus expectatus, and the chameleon Brookesia confidens (Glaw and Vences, 2007; Glaw et al., 2012). During a 2014 expedition to northern Madagascar, we found a single specimen of a morphologically unusual Madagascarophis while surveying a tsingy rock plateau at night in Ankarana National Park. Using multiple loci, we examine species boundaries of this new Malagasy cat-eyed snake in a Bayesian coalescent framework and provide a morphological description that discriminates this new species from others in the genus. We also determine the placement of the new species within Madagascarophis, infer a species tree that includes all currently recognized species, and produce a taxonomic key for all species in the genus. MATERIALS AND METHODS Collection and morphological data.—Snakes included in this study from the 2014 expedition (Appendix 1) were eutha- nized using an anesthetic, fixed in 80% ethanol, and stored in 70% ethanol, generally following the protocols of Simmons (2002). Whenever possible, hemipenes were evert- ed by injection and tied-off at their base. All vouchered specimens were assigned a RAX (C. J. Raxworthy field series) 1 Department of Herpetology, American Museum of Natural History, 200 Central Park West, New York, New York 10024; Email: (SR) sruane@ amnh.org, sararuane@gmail.com; (FTB) Burbrink666@gmail.com; and (CJR) rax@amnh.org. Send reprint requests to SR. 2 Museum of Natural Science, Louisiana State University, 119 Foster Hall, Baton Rouge, Louisiana 70803. 3 D´ epartement de Biologie Animale, Universit´ e de Mahajanga, BP 339 Mahajanga 401, Madagascar; Email: bernardzoo01@gmail.com. Submitted: 4 September 2015. Accepted: 8 March 2016. Associate Editor: B. Stuart. Ó 2016 by the American Society of Ichthyologists and Herpetologists DOI: 10.1643/CH-15-346 Published online: 1 September 2016 Copeia 104, No. 3, 2016, 712–721