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FIGURE 11 in The masked water snakes of the genus Homalopsis Kuhl & van Hasselt, 1822 (Squamata, Serpentes, Homalopsidae), with the description of a new species

FIGURE 11. Dorsolateral patterns of four species of Homalopsis, these are not completely reliable for identification but can provide clues to the identity of a species. A. H. buccata—there are four rows of dorsal scales between the ventrals and the bottom of the brown blotches; the blotches are not well outlined with black and in live specimens the pale and brown blotches are often subdued and low in contrast. B. H. semizonata has six dorsal rows (or more) between the ventrals and the bottom of the brown blotches. C. H. nigroventralis has all dorsal scale rows a dark olive gray with light colored bands extending to the ventrals. D. H. mereljcoxi sp. nov. has five dorsal scale rows between the ventrals and the bottom of the brown blotches; the dorsal pattern contains brown blotches that are usually outlined with black and the dorsal pattern is usually high contrast.

FIGURE 10 in The masked water snakes of the genus Homalopsis Kuhl & van Hasselt, 1822 (Squamata, Serpentes, Homalopsidae), with the description of a new species

FIGURE 10. Homalopsis semizonata. Left: the holotype of Homalopsis semizonata Blyth ZSI8137 showing its three prefrontal scales, fragmented frontal and divided loreal, photograph by CM. Right: the anterior crown of KU92453 showing the three prefrontals and the fragmented frontal scale.

FIGURE 9. Homalopsis nigroventralis. Above FMNH 263032 in The masked water snakes of the genus Homalopsis Kuhl & van Hasselt, 1822 (Squamata, Serpentes, Homalopsidae), with the description of a new species

FIGURE 9. Homalopsis nigroventralis. Above FMNH 263032 from Cambodia (Virachey National Park, O Kanome stream, 14°15'08.0" N, 106°37'58.8" E, 175 m) profile showing three upper labials at the loreal and that upper labial number 6 is the first horizontally divided labial. Note the dark coloration and the reduced "mask" in this specimen. Below: ventral view of FMNH 263029, also from Cambodia (Virachey National Park, O Lopeung stream, 14°10'39.2" N, 107°17'25.1" E, 150m), shows the reverse ventral pattern with a dark ground color and pale colored spots. Photographs JCM.

FIGURE 7. A in The masked water snakes of the genus Homalopsis Kuhl & van Hasselt, 1822 (Squamata, Serpentes, Homalopsidae), with the description of a new species

FIGURE 7. A. Homalopsis buccata from East Kalimantan, northeast of Samarinda, Kutai Kartanegara Regency, Kembangjanggut District (~25°30' N, 117°17' E). Photograph by Rob Steubing. Homalopsis mereljcoxi sp. nov. from the Khorat Basin, near Khon Kaen, Thailand (~16°01" N, 102°35' E). Photograph by JCM. The high contrast, evenly spaced, pale colored bands outlined in black that extend across the dorsum help distinguish this species from H. buccata which often have more irregular bands with less contrast. C. Homalopsis nigroventralis from an unknown locality in Thailand. Photograph by JCM. D. Homalopsis semizonata (CAS 242725) an adult from Myanmar: Tanintharyi Division: Dawei District: Yephyu Township: Tanintharyi Nature Reserve, Khotama stream, (14°44'08.3" N, 98°15'09.0" E, 73.1m); total length 860 mm. Photograph by Jens Vidum. This species has wide, gray blotches that do not go completely around the body.

FIGURE 5 in The masked water snakes of the genus Homalopsis Kuhl & van Hasselt, 1822 (Squamata, Serpentes, Homalopsidae), with the description of a new species

FIGURE 5. Map summarizing the distribution of the five species of Homalopsis. Known localities for H. nigroventralis are in black, known localities for H. mereljcoxi sp. nov. are in red. The area in yellow is the area inhabited by the family Homalopsidae. Question marks mark areas that are suspected of having Homalopsis based upon anecdotal observations in the literature or museum specimens with questionable data.

FIGURE 4 in The masked water snakes of the genus Homalopsis Kuhl & van Hasselt, 1822 (Squamata, Serpentes, Homalopsidae), with the description of a new species

FIGURE 4. Box whisker graphs comparing ventral and subcaudal scale count data for Homalopsis by gender. A. Among both males and females the only significant differences in ventral scale counts (p <0.05) are between H. mereljcoxi sp. nov. and the other three species. B. Among both males and females the only significant differences in subcaudal scale counts (p <0.05) are between H. semizonata and H. mereljcoxi sp. nov..

FIGURE 3. A in The masked water snakes of the genus Homalopsis Kuhl & van Hasselt, 1822 (Squamata, Serpentes, Homalopsidae), with the description of a new species

FIGURE 3. A cluster analysis of 95 specimens of Homalopsis. The data set used was the same as that used for the PCA and included: dorsal scale row counts on the forebody, midbody, posterior body; number of prefrontals, preoculars, postoculars, upper labials; upper labials under orbit; upper labials at loreal; loreal condition (single, divided, or fragmented); and ventral pattern. Specimens are listed by museum number with a prefix for the species they represent: hb = H. buccata, hh = H. hardwickii, hn = H. nigroventralis, hm = H. mereljcoxi (new species) hs = H.semizonata.

FIGURE 1 in The masked water snakes of the genus Homalopsis Kuhl & van Hasselt, 1822 (Squamata, Serpentes, Homalopsidae), with the description of a new species

FIGURE 1. Ocular ring morphology in five species of Homalopsis. Scale nomenclature: 1 = preocular, 2 = presubocular, 3 = subocular, 4 = postsubocular, 5 = postocular. A. H. buccata: preocular(s) one or two, presubocular one, subocular(s) present about 50% of the time, postocular(s) one or two, postsubocular one (but may be absent). B. H. hardwickii has the lowest number of scales in the ocular ring of any specimen (or species) examined: preocular one, presubocular not present, subocular not present (upper labial in orbit), postocular one, postsubocular one. C. H. mereljcoxi: preocular one, presubocular one (but may be absent), suboculars two or three (rarely absent or four), upper labial six rarely present in orbit, postoculars two (rarely one), postsubocular one (rarely absent). D. H. nigroventralis has the largest number of scales in the ocular ring: preocular one, presubocular one, suboculars one or two (rarely three), postoculars two or three, postsubocular one. E. H. semizonata has the most consistent number of scales in the ocular ring: preocular one (rarely two), presubocular one, subocular one (rarely does a lower labial enter the orbit as it does in the photo), postocular one, postsubocular one.

FIGURE 2 in The masked water snakes of the genus Homalopsis Kuhl & van Hasselt, 1822 (Squamata, Serpentes, Homalopsidae), with the description of a new species

FIGURE 2. Plots of the principal components (PC) scores on the first two PC axes derived from 11 morphological variables (dorsal scale row counts on the forebody, midbody, posterior body; number of prefrontals, preoculars, postoculars, upper labials; upper labials under orbit; upper labials at loreal; loreal condition; ventral pattern) for 95 specimens of Homalopsis. The square with the central circle is H. hardwickii which associates with H. buccata in this analysis. Plot A compares H. buccata, H. mereljcoxi, and H. hardwickii; Plot B compares H. buccata, H. mereljcoxi, H. hardwickii, and H. semizonata; Plot C compares all five species: H. buccata, H. mereljcoxi, H. hardwickii, H. semizonata, and H. nigroventralis.

FIGURE 4 in Taxonomic identity of two enigmatic aquatic snake populations (Squamata: Homalopsidae: Cerberus and Homalopsis) from southern Thailand

FIGURE 4. Nine live newborn Homalopsis semizonata; their mother is QSMI 1390 from Muang District, Ranong Province. Photograph by M. Sumontha.

FIGURE 3 in Taxonomic identity of two enigmatic aquatic snake populations (Squamata: Homalopsidae: Cerberus and Homalopsis) from southern Thailand

FIGURE 3. General ventral view of an adult Homalopsis semizonata (QSMI 1390) from Muang District, Ranong Province. Photograph by O.S.G. Pauwels.

FIGURE 2 in Taxonomic identity of two enigmatic aquatic snake populations (Squamata: Homalopsidae: Cerberus and Homalopsis) from southern Thailand

FIGURE 2. Dorsal head view of a preserved adult Homalopsis semizonata (QSMI 1389) from Muang District, Ranong Province, showing a frontal scale divided into five parts, three internasals and two prefrontals. Photograph by O.S.G. Pauwels.

FIGURE 1 in Taxonomic identity of two enigmatic aquatic snake populations (Squamata: Homalopsidae: Cerberus and Homalopsis) from southern Thailand

FIGURE 1. General laterodorsal view of a preserved adult Homalopsis semizonata (QSMI 1389) from Muang District, Ranong Province. Photograph by O.S.G. Pauwels.

FIGURE 8 in The masked water snakes of the genus Homalopsis Kuhl & van Hasselt, 1822 (Squamata, Serpentes, Homalopsidae), with the description of a new species

FIGURE 8. Homalopsis mereljcoxi sp. nov., holotype FMNH 263756. Details of scalation.

FIGURE 6 in The masked water snakes of the genus Homalopsis Kuhl & van Hasselt, 1822 (Squamata, Serpentes, Homalopsidae), with the description of a new species

FIGURE 6. Homalopsis buccata, neotype, FMNH 250114 from Singapore.

FIGURE 6 in Taxonomic identity of two enigmatic aquatic snake populations (Squamata: Homalopsidae: Cerberus and Homalopsis) from southern Thailand

FIGURE 6. Live subadult male from Phuket Province, detail of head. Photograph by M. Sumontha.

FIGURE 5 in Taxonomic identity of two enigmatic aquatic snake populations (Squamata: Homalopsidae: Cerberus and Homalopsis) from southern Thailand

FIGURE 5. Live subadult male from Phuket Province, general view in situ. Photograph by M. Sumontha.