In this first paper of a series of three, the taxonomy of the Asian pitvipers of the genus Tropidolaemus is re-evaluated on the basis of morphological analyses. Variation in morphological characters was investigated on the basis of specimens from the whole range of the pitviper currently known as Tropidolaemus wagleri (Boie, 1827). Our results, based on morphological univariate and multivariate analyses, define three clusters of populations that are morphologically diagnosable and which are here considered to represent distinct species following the Biological Species Concept and the Phylogenetic Species Concept. After a review of available names among the list of synonyms created during the confused taxonomical history of the genus Tropidolaemus, it appears that Tropidolaemus wagleri (Boie, 1827) is the valid name of the first cluster which includes populations inhabiting Southern Thailand, West Malaysia, Sumatra, Nias, Mentawei Archipelago and Bangka Island (but not Belitung). In order to stabilize the binomen, we select and describe a neotype for Tropidolaemus wagleri. A second cluster, for which the binomen Tropidolaemus subannulatus (Gray, 1842) isavailable, includes in this preliminary step populations from Borneo, Sulawesi, Sulu Archipelago and the Philippines. Its detailed taxonomy will be addressed in the second paper of the series. Lastly, the third cluster includes specimens from Mindanao Island, Philippines, recognized here as Tropidolaemus philippensis (Gray, 1842).KEY WORDS: Indonesia, Thailand, West Malaysia, Sumatra, Borneo, Sulawesi, Philippines, Serpentes, Viperidae, Tropidolaemus, Tropidolaemus wagleri, Tropidolaemus subannulatus, Tropidolaemus philippensis, Tropidolaemus laticinctus, Tropidolaemus huttoni, taxonomy, neotypeAmong pitvipers of tropical Asia, members of the genus Tropidolaemus Wagler, 1830 are among the most widespread and often commonly encountered venomous snakes in many islands of the Indo-Malayan Archipelago. Long regarded as a synonym or a subgenus of Trimeresurus (see, for example, Brattstrom, 1964), the genus Tropidolaemus was resurrected by Burger (1971) to then accommodate the sole species formerly called Trimeresurus wagleri. The validity of the genus is accepted by all recent authors. This genus is characterized by the absence of a nasal pore, upper surfaces of the snout and head covered with distinctly keeled small scales, strongly keeled gular scales, second supralabial not bordering the anterior margin of the loreal pit and topped by a prefoveal, and a green coloration in juveniles which may or may not change with growth. For long, Tropidolaemus wagleri was the sole species included in the monotypic genus, but David & Vogel (1998) showed that the Indian species Trimeresurus huttoni Smith, 1949 was clearly a member of this genus. In this first paper of a series of three, we address the rather confused nomenclatural history and taxonomy of Tropidolaemus wagleri (Boie, 1827) sensu auctorum (see, for example, David & Ineich, 1999; McDiarmid et al., 1999; Gumprecht et al., 2004). Members of this species complex are widespread throughout the IndoMalayan part of Asia, with an isolated population in Southern Vietnam. Besides this latter country, it is distributed from southern Thailand to the Philippines and Sulawesi Island, including West Malaysia, and the islands of Sumatra, Borneo, Bangka, Nias, the Mentawai Archipelago, and Belitung. Although a common and conspicuous, very variable species, few authors tried to investigate its taxonomy, most probably following Boulenger (1896) who synonymised the various names under the sole specific name Lachesis wagleri. Nevertheless, Taylor (1917, 1922) examined Philippine populations and recognized three subspecies, of which two were considered endemic to the Philippine islands, Tropidolaemus wagleri alboviridis (Taylor, 1917) and T. wagleri subannulatus (Gray, 1842). This position was not accepted by Leviton (1964), who investigated the taxonomy of the Philippine populations and considered again Tropidolaemus wagleri to be monotypic. However, Leviton added: “The exact status of the nominal species and subspecies I have placed into the synonymy of T. wagleri cannot be settled until the type specimens and additional material from scattered localities can be examined.” The monotypic status of Tropidolaemus wagleri was accepted by subsequent authors (Harding & Welch, 1980; Hoge & Romano-Hoge, 1981; Alcala, 1986; Welch, 1988; Golay et al., 1993; David & Vogel, 1996, Manthey & Grossmann, 1997; McDiarmid et al., 1999), although some noted that the taxonomy of the species was unsatisfactory (David & Ineich, 1999). David & Vogel (1998) discussed the taxon described as Trimesurus philippensis Gray, 1842, regarded as valid by Taylor (1922) and Maslin (1942) as Trimeresurus philippinensis, but placed in the synonymy of Tropidolaemus wagleri by Leviton (1964), who, however, seemingly did not examine its holotype. David & Vogel (1998) examined two specimens, namely the holotypes of Trimeresurus philippensis Gray, 1842 and Tropidolaemus hombronii Jacquinot & Guichenot, 1848, clearly a synonym of the former one. David & Vogel (1998) and David & Ineich (1999) noted that both specimens displayed notable morphological differences (scalation of head and body and coloration) with Tropidolaemus wagleri.

The group of Asian colubrid species morphologically similar to Oligodon taeniatus (Günther, 1861), previously containing only O. taeniatus, Oligodon mouhoti (Günther, 1864) and Oligodon barroni (Smith, 1916), is revised on the basis of variation in external morphology and dentition of 175 specimens. The confused nomenclatural history of O. taeniatus and its name bearing type is discussed. A neotype is described for Simotes quadrilineatus Jan & Sordelli, 1865, a synonym of O. taeniatus. The holotype of Simotes taeniatus var. mouhoti Boulenger, 1914 is identified. Three new species within this group are described. Oligodon pseudotaeniatus spec. nov. is described on the basis of specimens from central Thailand. This species is morphologically similar to Oligodon taeniatus, but differs by the combination of 17 dorsal scale rows at midbody, 8 supralabials, the absence of dark dorsal and tail blotches and the presence of a vertebral stripe edged with black but no dorsolateral stripes. Oligodon deuvei spec. nov. is described on the basis of specimens from southern Vietnam and Laos; it differs from other known species of the group by the combination of 12–15 maxillary teeth, 17 dorsal scale rows at midbody, usually seven supralabials, the absence of dark dorsal and tail blotches and the presence of a broad vertebral stripe, often conspicuously orange or rusty red. This species is most similar to Oligodon barroni but differs from the latter by a higher number of maxillary teeth and the absence of dark dorsal and tail blotches. Lastly, Oligodon moricei spec. nov. is described on the basis of a single specimen from southern Vietnam. It differs from other species by the combination of a broad rusty brown vertebral stripe edged with two broad black stripes, 12 maxillary teeth, 17 dorsal scale rows, a high number of ventral scales, seven supralabials and a dark cloudy or smoky venter. These new species are compared with other species known from the Indo-Chinese Region. The diagnoses of O. taeniatus, O. mouhoti and O. barroni are revised. A key to members of the group is given.

A new species of the colubrid genus Dendrelaphis Boulenger 1890 is described. Dendrelaphis kopsteini sp. nov. ranges from Thailand through Peninsular Malaysia and Singapore to Sumatra. A detailed statistical analysis of the differences between D. kopsteini sp. nov., D. formosus (Boie, 1827) and D. cyanochloris (Wall, 1921) is provided as the three species have been mixed up frequently in the literature. D. kopsteini sp. nov. differs from all other Dendrelaphis species by a brick red neck coloration. A neotype is designated and described for D. formosus and a lectotype is designated and described for D. cyanochloris.

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Three species of the genus Amphiesma Duméril, Bibron & Duméril, 1854 have long been confused in the literature, with each other and with other species of the genus. Amphiesma khasiense (Boulenger, 1890) has been considered to inhabit a large geographical region, extending from northeastern India, east to Vietnam and southern Thailand. Amphiesma boulengeri (Gressitt, 1937) has been regarded as a species endemic to southeastern China. Amphiesma inas (Laidlaw, 1901) has been recorded from West Malaysia, Thailand and Indonesia (Sumatra). A multivariate analysis of morphometric and meristic characters shows that these three species can be separated by combinations of characters in the scalation and pattern, the most obvious being the structure of the postocular streak. On the basis of our analysis and after comparison with name-bearing type specimens, Amphiesma khasiense is restricted to northeastern India, Myanmar, western Yunnan Province of China, northern Laos and northern and western Thailand. Other populations from southeastern China, Vietnam, other parts of Laos, Cambodia and central Thailand, which have been recorded in the literature as A. khasiense, A. johannis or Amphiesma modestum (Günther, 1875), should be referred to Amphiesma boulengeri. Amphiesma inas (Laidlaw, 1901) is a valid species endemic to mountain ranges of southern Peninsular Thailand and West Malaysia. The mention of Amphiesma inas in Sumatra is erroneous, being based on the second known specimen of Amphiesma kerinciense David & Das, 2003, which is here redescribed. A key to species of the Amphiesma khasiense group and other species sharing a greyish-brown background without conspicuous dark and pale stripes, is provided.