Despite recent progress in our understanding of diversity within the genus Trimeresurus Lacépède, 1804, the subgenus Popeia Malhotra & Thorpe, 2004, distributed across most parts of East and Southeast Asia, remains taxonomically challenging. We applied an integrative taxonomic approach including analyses of morphological data and four mitochondrial genes (12S and 16S rRNA, cytochrome b, and NADH dehydrogenase subunit 4), along with examination of available type material, to address longstanding taxonomic questions in one clade within Popeia, the T. popeiorum group, and reveal a high level of hidden diversity of these snakes in the Indo-Burma Biodiversity Hotspot. We confirm that T. popeiorum Smith, 1937 sensu stricto is restricted to Northeast India, eastern Nepal, southern Bhutan, southeastern Bangladesh, western Yunnan Province (China), and northern and southwestern Myanmar. We further confirm that the recently described species T. yingjiangensis Chen et al., 2019 is a junior synonym of T. popeiorum. In addition, we discovered that the combination Trimesurus [sic] elegans Gray, 1853 is a valid senior synonym of T. popeiorum and threatens the stability of the latter taxon. Therefore, in order to protect the nomen popeiorum and in accordance with Article 23.9 of the International Code of Zoological Nomenclature, we regard the taxon Trimesurus elegans as a nomen oblitum and render Trimeresurus popeiorum a nomen protectum. Examination of a larger series of specimens allows us to describe two new cryptic species of Trimeresurus from the Indo-Burma Region. This study brings the total number of species in the subgenus Popeia to six and also suggests that the subspecific taxonomy of the T. sabahi complex requires further investigation. We urge adequate actions regarding the conservation of the newly discovered species and recommend further studies on their toxicology.

Variation in morphological characters were investigated among 136 specimens (128 specimens examined by us and eight specimens described in the literature) from 44 populations of the whole range of the pitviper currently known as Trimeresurus popeiorum Smith, 1937. Univariate and mul-tivariate analyses of these morphological characters allowed us to recognize six clusters of populations that are morphologically diagnosable, and that are here considered to represent independent lineages. Five of these clusters are considered to be distinct species following the Biological Species Concept and the Phylogenetic Species Concept. Two of them are described as new. Trimeresurus fucatus spec. nov. includes populations from southern Thailand and most of West Malaysia. Trimeresurus nebularis spec. nov. is described for populations from Cameron Highlands of West Malaysia. A population from Toba Massif, northern Sumatra, is referred to this complex, but cannot be assigned to a species at the present time. Trimeresurus popeiorum sabahi is raised to specific status, Trimeresurus sabahi new comb., to accommodate the populations from Borneo, whereas Trimeresurus barati new comb. includes the populations from western Sumatra and the Mentawai Archipelago. Separate keys to the two sexes of the recognised species of the T. popeiorum complex are provided.KEY WORDS: Thailand, West Malaysia, Sumatra, Borneo, Serpentes, Viperidae, Trimeresurus, Trimeresurus popeiorum, Trimeresurus fucatus spec. nov., Trimeresurus nebularis spec. nov., Trimeresurus sabahi, Trimeresurus baratiBefore the paper by Pope & Pope (1933), all green Trimeresurus species were gathered under the name Trimeresurus gramineus (Shaw, 1802). In a first step towards understanding the systematics of the genus, these authors split the nominal taxon gramineus into six species. The specific nomen gramineus was applied to a widespread species, ranging from northeastern India to western Indonesia. Indian populations were referred to a new species described as Trimeresurus occidentalis. Subsequently, Smith (1937) correctly showed that Pope & Pope (1933) misunderstood the type locality of gramineus, and showed that the type locality for T. gramineus was within the range of T. occidentalis. Therefore, Trimeresurus occidentalis Pope & Pope 1933 became a subjective junior synonym of T. gramineus (Shaw, 1802), leaving unnamed the distinct eastern taxon. Smith (1937) named it as Trimeresurus popeiorum. Unfortunately, he failed to designate a type specimen and a type locality for this new taxon. This interpretation was accepted by most subsequent authors except Hoge & Romano Hoge (1981) and Welch (1988). Another issue affecting the specific nomen is its spelling. Smith (1943) corrected the original spelling as popeorum on the basis that it was indeed a clerical error. This spelling was largely accepted, and was the subject of recent controversies. This problem will be addressed in another paper (David & Vogel, submitted). We consider that the correct spelling is indeed popeiorum. Eventually, Taylor & Elbel (1958), regarded as syntypes of Trimeresurus popeiorum Smith, 1937 all specimens referred by Pope & Pope (1933) to as T. gramineus, and designated the specimen BMNH 72.4.17.137 as the lectotype of the species. Consequently, the type locality was restricted to Khasi Hills, Assam , now in the State of Meghalaya, India.

Slug-eating snakes of the subfamily Pareinae are an insufficiently studied group of snakes specialized in feeding on terrestrial mollusks. Currently Pareinae encompass three genera with 34 species distributed across the Oriental biogeographic region. Despite the recent significant progress in understanding of Pareinae diversity, the subfamily remains taxonomically challenging. Here we present an updated phylogeny of the subfamily with a comprehensive taxon sampling including 30 currently recognized Pareinae species and several previously unknown candidate species and lineages. Phylogenetic analyses of mtDNA and nuDNA data supported the monophyly of the three generaAsthenodipsas,Aplopeltura, andPareas. Within bothAsthenodipsasandPareasour analyses recovered deep differentiation with each genus being represented by two morphologically diagnosable clades, which we treat as subgenera. We further apply an integrative taxonomic approach, including analyses of molecular and morphological data, along with examination of available type materials, to address the longstanding taxonomic questions of the subgenusPareas, and reveal the high level of hidden diversity of these snakes in Indochina. We restrict the distribution ofP. carinatusto southern Southeast Asia, and recognize two subspecies within it, including one new subspecies proposed for the populations from Thailand and Myanmar. We further revalidateP. berdmorei, synonymizeP. menglaensiswithP. berdmorei, and recognize three subspecies within this taxon, including the new subspecies erected for the populations from Laos and Vietnam. Furthermore, we describe two new species ofPareasfrom Vietnam: one belonging to theP. carinatusgroup from southern Vietnam, and a new member of theP. nuchalisgroup from the central Vietnam. We provide new data onP. temporalis, and report on a significant range extension forP. nuchalis. Our phylogeny, along with molecular clock and ancestral area analyses, reveal a complex diversification pattern of Pareinae involving a high degree of sympatry of widespread and endemic species. Our analyses support the “upstream” colonization hypothesis and, thus, the Pareinae appears to have originated in Sundaland during the middle Eocene and then colonized mainland Asia in early Oligocene. Sundaland and Eastern Indochina appear to have played the key roles as the centers of Pareinae diversification. Our results reveal that both vicariance and dispersal are responsible for current distribution patterns of Pareinae, with tectonic movements, orogeny and paleoclimatic shifts being the probable drivers of diversification. Our study brings the total number of Pareidae species to 41 and further highlights the importance of comprehensive taxonomic revisions not only for the better understanding of biodiversity and its evolution, but also for the elaboration of adequate conservation actions.

The white-lipped tree viper, Trimeresurus albolabris Gray, is one of the most common species of the genus Trimeresurus with a wide distribution from India eastwards to China and southwards to Indonesia. However, this species was previously split into five geographical clades with significant genetic divergence. Recent surveys in Yingjiang County, Yunnan Province, China resulted in the discovery of one cryptic species of the subgenus Trimeresurus. Combining molecular, morphological and ecological data, we describe it as a new species Trimeresurus caudornatus sp. nov. The new species differs from other Trimeresurus species by a combination of the following characteristics: (1) Head and body generally dark green, postocular stripes absent in both genders, upper labials light green; (2) ventrolateral stripe faint green yellow, present on the first row of DSR in both genders; (3) iris golden yellow in both genders; (4) dorsal tail mostly dark red, lateral and ventral green; an orange red stripe along the ventral part of the tail; (5) DSR 21/22 –21–15, VEN 161–163, SC 52–72; (6) first upper labial partially fused to the nasal. The new species was shown to be a strongly supported monophyletic group (BPP 100%) and sister to T. septentrionalis. The uncorrected pairwise distances of mitochondrial gene Cytb between the new species and other species of the subgenus Trimeresurus, ranging from 0.059 (T. septentrionalis) to 0.134 (T. kanburiensis).

Species of the genus Hebius Thompson, 1913 with 17 or 19 dorsal scale rows at midbody and an overall dark venter are reviewed, including the two species previously known as Parahelicops annamensis Bourret, 1934 and Pararhabdophis chapaensis Bourret, 1934. Specimens with 17 scale rows are morphologically similar to Hebius venningi (Wall, 1910), which is here redefined based on external morphological characters such as scalation, and dorsal and ventral patterns. Consequently, Natrix nigriventer Wall, 1925 is resurrected from its synonymy with Hebius venningi, whereas Natrix taronensis Smith, 1940, previously considered a subspecies of H. venningi or a full species by some authors but without justification, is here confirmed to full species status. Another group of species, mostly similar in coloration and pattern to the H. venningi group but with 19 dorsal scale rows, includes H. modestus (Günther, 1875), H. deschauenseei (Taylor, 1934) and a new species which is described herein based on specimens from northern Vietnam, southern China and north-eastern Thailand due to distinct morphological differences. We also provide updated taxonomic accounts for the species of this group, including an identification key and distribution maps.

We revisit the identities of ‘Trimeresurus albolabris’ records from India and Nepal, based on a re-examination of historically mentioned specimens. Based on morphological congruence, we identify an old specimen originally labeled as T. albolabris from ‘Nagpur, Central Province’ as Trimeresurus salazar. We also provide new records of T. salazar based on molecular data from newly collected specimens in Central India. As the range of T. salazar is now known to approach that of its sister species Trimeresurus septentrionalis, we also redescribe T. septentrionalis based on the holotype and referred material. Finally, we examined two historical specimens from “Madras” collected during the Novara Expedition, which we identify as T. davidi, leading to a reassessment of their origin. Consequently, we remove T. albolabris from the list of Indian snake fauna.