Description. An adult female, 487 mm in total length; tail lenght 48 mm (9.9% of total); head length 16.3 mm from front face of rostral to posterior end of mandible; head width 11.2 mm at broadest point at the rictus; head moderately distinct from neck; nout rounded in dorsal view; eye small, snout 3.0 times as long as horizontal distance across eye; pupil round; rostral about 1.2 times broader than high; internasals 1.4 times wider than long, contacting anterior and posterior nasals laterally; prefrontals large, slightly longer than wide, contacting posterior nasal and loreal laterally; median prefrontal suture 0.6 times as long as frontal; frontal as broad as long; parietals about 1.6-1.8 times longer than wide, median suture 1.1 times frontal length; nostrils located in anterior nasal; loreal about equal to conmbined length of nasals; preocular absent; supraocular large, 1.1. times longer than loreal; two postoculars; temporals 1-1, separating supralabials 6 and 7 from parietal; supralabials 7/7, 1 contacting nasals, 2 contacting postnasal and loreal, 3 contacting loreal, 3 and 4 entering orbit, 5 and 6 contact anterior temporal, 6 largest and contacting posterior temporal; mental 3.8 times broader than long, separated from chin shields by first infralabials which contact each other along midline; chin shields well developed, about twice as long as wide and not extending to border of lip; posterior chin shields not differentiated from gulars; anterior chin shields separated from first ventral by four gulars; infralabials 7/7, 1-4 contacting anterior chin shield, foruth largest; unreduced dorsal scales in 15 smooth rows throughout length of body; dorsal scales in 6 rows at the level of the tenth subcaudal; no apical pits apparent; ventrals 133; anal divided; subcaudals 21, paired; anal glands paired, extending 2 subcaudals.

Diagnosis. The new species is a member of the verapacis group that can be distinguished from all other members of the group by its large size, females attain lenghts of at least 574 mm and males probably exceed 400 mm; broad frontal plate, at least as broad as long; dorsal coloration dark brown suffused with black; relatively small eye, contained 2.7-3.2 times in the snout length; low number of dentary teeth, 8-9.

Especie endémica de Guatemala.

Centro de Estudios Conservacionistas [Cecon]. Catálogo de autoridades taxonómicas de la fauna de Guatemala. [Rastreo de Elemento:Vertebrata]. Centro de Datos para la Conservación (CDC), Centro de Estudios Conservacionistas (Cecon), Facultad de Ciencias Químicas y Farmacia, Universidad de San Carlos de Guatemala. Guatemala. Ver versión aquí: tinyurl.com/catcdc.

Morales-Mérida, J.R., Muller, F. (2020). New record of Adelphicos dayi (Serpentes: Dipsadidae) after 19 years, and additional record of Ptychohyla euthysanota (Anura: Hylidae) in Guatemala. Amphibian & Reptile Conservation 14(3) [General Section]: 57-61.

Campbell J.A., Ford L.S. (1982). Phylogenetic relationships of the colubrid snakes of the genus Adelphicos in the highlands of Middle America. Occasional Papers of the Museum of Natural History University of Kansas 100: 1–22.

Assessed as Endangered B1ab(iii), ver. 3.1; date assessed: 7 May 2012