Taxonomic review of the rare Mexican snake genus Chersodromus (Serpentes: Dipsadidae), with the description of two new species Author Canseco-Márquez, Luis Author Ramírez-González, Cynthia G. Author Campbell, Jonathan A. text Zootaxa 2018 2018-03-21 4399 2 151 169 journal article 30456 10.11646/zootaxa.4399.2.1 834234e8-ac96-4b19-a30e-3edc31fe4897 1175-5326 1206522 43A975F2-05F6-4A29-A588-7787AF63589C Chersodromus liebmanni Reinhardt, 1860 Fig. 2 , 3A , Table 1 Chersodromus liebmanni Reinhardt, 1861 , Vidensk. Meddel. Naturhist. Foren. Kjöbenhavn 2:243. Holotype : ZMUC 60561 . Type-locality: “ Mexico . ” Restricted to Cuautlapan, Veracruz , Mexico , by Smith & Taylor (1950:347), and to Mirador, Veracruz , Mexico by Smith & Braestrup (1963:240). Chersodromus nigricans Reinhardt, 1861 Vidensk. Meddel. Naturhist. Foren. Kjöbenhavn 2:245. Holotype : ZMUC 60562 . Type locality: “ Mexico . ” Restricted to Cuautlapan, Veracruz , Mexico , by Smith & Taylor (1950:347), and to Mirador, Veracruz , Mexico by Smith & Braetrup (1963:240). Opisthiodon torquatus Peters, 1861 , Monatsber. königl. Akad. Wiss. Berlin. 1861:461. Holotype : Berlin Museum. Type locality: Huanusco [= Huatusco ], Veracruz . Dirosema collare Werner 1900 , Zool. Anz. 23:197. Holotype : Not traced. Type-locality: Mexico . Diagnosis. Chersodromus liebmanni can be distinguished from all Mexican species of snakes by having combination of prefrontals fused into single scale; postocular fused with supraocular; dorsal scales keeled in 17 rows at midbody, unreduced posteriorly; supralabials 7, third and fourth entering orbit; infralabials 7–8, usually 1– 5 contacting anterior chinshields (5 narrowly); mental contacting anterior chinshields; venter cream colored. This species may be distinguished from all species of Chersodromus , except C. rubriventris , by having the postocular fused with supraocular; from C. rubriventris by having 17 scales around body (vs. 15), ventral surface uniformly cream (vs. bright orange) ( Table 1 ). Ninia diademata Baird & Girard (1853) might be confused with this species, and they are sympatric at some localities in Oaxaca and Veracruz . Ninia diademata differs from Chersodromus in having paired prefrontals shields, 19 strongly keeled dorsal scale rows, and two postoculars, larger body size (reaching at least 330 cm TL), and more slender tail. Description. Small, slender snake; head moderately wider than the neck. Adults commonly reaching 250–330 mm in total length with the largest known male 310 mm , and the largest female 330 mm . Tail comprises 16–22% of total length in males, 15–18% in females. FIGURE 2. Dorsal (A), ventral (B) and lateral (C) views of the head (Scale = 3 mm); right maxilla (D, 2.61 mm); and from left to right: sulcate, lateral, and asulcate views of the hemipenis (E–G, Scale = 3.9 mm) of Chersodromus liebmanni (MZFC 28687). FIGURE 3. Adult of Chersodromus liebmanni in life (MZFC 28687) from Totontepec, Oaxaca (A), and its locality in Cuautlapan, Veracruz (B). Prefrontals fused into a single, large scale. Supraoculars fused with postoculars. Frontal relatively broad and nasals divided. Small internasals 1/1, loreals 1/1, extending from the postnasal to the anterior edge of eye (no preoculars). No discrete postoculars are present (fused with supraocular). temporals 1+2 (rarely 1+1 owing to fusion of secondary series), supralabials 6–7 (usually 7) with 3–4 entering orbit, infralabials 6–8 (usually 7) with 1–4 contacting anterior chinshields (5 usually narrowly). Mental broader than long, first pair of infralabials not in contact along ventral midline. Anterior chinshields large with posterior pair of chinshields about one-third to onehalf the size and anterior pair. Dorsal scales keeled in 17-17-17 rows, rarely reduced by one either anteriorly or posteriorly. Preventrals 2 (rarely 1), ventrals 121–136 in males and 126–140 in females; divided subcaudals 32–42 in males and 31–39 in females; dorsal scale rows at midlength of tail 6–8. Cloacal scute undivided. Pupil subcircular to vertically oval. A conspicuous yellow collar crosses the back of the head; the anterior border is irregular, usually having a middorsal forward extension to near the posterior tip of the frontal, extending on either side to involve about onehalf to two-thirds of the parietals, and laterally including the posterior portion of the anterior temporal and secondary temporals and portions of last several supralabials. Posterior border of the collar relatively straight, reaching the posterior edges of the parietals or nearly so, and extending posteriorly 0.5–1 scales. Dorsum dark gray to blackish and extends to the lateral portion of ventrals and subcaudals. A black head cap extends from the rostral to the anterior portion of parietals, covering internasals, a single fused prefrontal, supraoculars and fused postoculars, nasals, loreal, anterior portion of anterior temporal, and upper portion or edges of at least supralabials 3–5. The mental and infralabials 1–4 often have dark speckling or mottling. Belly immaculate cream or with varying amounts of dark mottling, especially along the midventer. Subcaudals usually have irregular dark mottling, especially along the midventer, and often become more heavily mottled posteriorly with distal portion of tail sometimes mostly dark. In a few individuals all subcaudals are mostly dark. Maxillary dentition ( Fig. 2 D ). Right maxilla extending anteriorly to level of suture between second and third supralabials, dorsoventrally compressed; in lateral view, anterior one-third curved dorsally; posterior end curved ventrally; maxillary teeth 7, slender, curved, longer posteriorly. Hemipenis morphology ( Fig. 2 E–G ). Retracted organ extends to level of tenth subcaudal, slightly bilobed, and semicapitate, sulcus spermaticus centrifugal with laterally expanded margins, ornamented with numerous spines of equal size, extending to tips of lobes; sulcus spermaticus bifurcates for about half length of hemipenial body; intrasulcar region and hemipenial body covered more-or-less homogeneously by spines, but on sulcate side of base, hook-shaped spine present on the right side of the hemipenis. In sulcate view, spines organized in inverted “V” shape before reaching capitation of hemipenis. On proximal region, two parallel folds protruding from body of hemipenis, ornamented by small spinules. Distribution and habitat. Inhabiting the Atlantic foothills and versant of west-central Veracruz in the Orizaba region southward through the Sierra Zongolica to Sierra Negra in southeast Puebla and the Sierra Mixe in northern Oaxaca ( Fig. 1 ). Chersodromus liebmanni inhabits upper rain forest and cloud forest ( Fig. 3B ) between 1000–1800 m above sea level (asl hereafter). Several specimens have been collected in agricultural fields and shade coffee plantations.