Chersodromus nigrum

description

Description of the holotype. Adult male; head length 9.07 mm; snout-vent length 260 mm; tail 74 mm; the tail comprises 22 % of total length in males, 18 – 20 % in females; head slightly distinct from neck; snout long, 2.5 times head length, rounded in dorsal aspect, projecting anteriorly beyond lower jaw; rostral 0.4 times broader than high, 2.7 times longer than internasal suture, with anterior end at level of anterior margin of nares; internasals broader than long (length vs breadth on L / R sides 0.63 / 0.57), rounded anteriorly, in contact laterally with anterior and posterior nasals; prefrontals fused, posterior corner contacting eye; postnasal plus loreal length 0.6 times length of snout, their common suture 0.2 times frontal length; frontal wider than long (length / breadth 0.8); supraocular fused with postocular; parietals 1.6 times longer than wide, approximately 0.5 times head length, parietal suture 1.1 times as long as frontal; large postocular on each side; nasal divided; postnasal 1.0 times as long as prenasal; combined length of prenasal and postnasal 2.2 times longer than loreal length; loreal 1.5 times wider than long, 3.7 / 3.4 times snout length, 1.1 times longer

Taxonomic review of the rare Mexican snake genus Chersodromus (Serpentes: Dipsadidae), with the description of two new species

diagnosis

Diagnosis. Chersodromus nigrum can be distinguished from all Mexican species of snakes by having combination of prefrontals fused into single scale; postocular fused with supraocular; single anterior temporal present; dorsal scales keeled in 17 rows at midbody, unreduced posteriorly; supralabials 6, third and fourth entering orbit; infralabials 8, 1 – 5 contacting anterior chinshields); mental contacting anterior chinshields; venter mostly black. This species is characterized by its large size (260 - 315 mm SVL). It differs from Chersodromus rubriventris and C. australis by having fused supraocular and postocular scales; distinguished from C. australis and usually C. liebmanni by having first 5 or 6 infralabials in contact with anterior chinshield (vs. 4 – 5), further differing from C. liebmanni by having six supralabials (vs. seven) (Table 1).

Taxonomic review of the rare Mexican snake genus Chersodromus (Serpentes: Dipsadidae), with the description of two new species

distribution

Distribution and habitat. This species is occurs in the cloud forests of the Sierra Madre Oriental of northern Puebla (Fig. 1 and 9 C) at elevations between 1493 – 1560 m asl. Other species of amphibians and reptiles recorded in the area include, Chiropterotriton sp., Charadrahyla taeniopus (Günther 1901), Craugastor rhodopis (Cope 1867), Rheohyla miotympanum (Cope 1862), Diploglossus legnotus Campbell & Camarillo 1994, Scincella silvicola (Taylor 1937) and Geophis sp.

Taxonomic review of the rare Mexican snake genus Chersodromus (Serpentes: Dipsadidae), with the description of two new species

etymology

Etymology. The specific name is from Latin nigrum, meaning black, alluding at to the coloration of the dorsal and ventral surface.

Taxonomic review of the rare Mexican snake genus Chersodromus (Serpentes: Dipsadidae), with the description of two new species