Recent studies on the systematics and phylogeny of the blue-tailed skinks in the Plestiodon brevirostris group identified a population from the Sierra Madre del Sur of eastern Guerrero, Mexico, that appeared to represent an undescribed species. Here, we formally describe this lineage as a new species, compare it with the other species in the P. brevirostris group, identify a specimen from western Oaxaca that belongs to the new species, and provide an updated key to the group. The new species is morphologically similar and closely related to P. ochoterenae , but molecular and morphological data support its evolutionary independence. The new species is distinguished from the other species in the P. brevirostris group, except for P. ochoterenae , by the presence of a primary temporal, a well-defined lateral pale line on the neck, and a well-defined dorsolateral pale line that extends posteriorly to the level of the hind limbs. It differs from P. ochoterenae by having longer limbs and a well-defined lateral pale line on the neck. The present study further highlights the relevance of the Sierra Madre del Sur as a hotspot of endemism and undescribed diversity.

A new species of the colubrid genus Geophis from northern Puebla, Mexico, is described. The new species possesses most of the diagnostic characters of the G. dubius group but differs from all other species of Geophis by having the loreal shorter than the combined prenasal and postnasal length, one postocular scale, one supraocular scale, the fifth supralabial and parietal in contact, dorsal scales in 17 rows, dorsal scales smooth throughout the length of the body or, if keeled, not anteriorly to the posterior fourth of the body, 129–140 ventrals in females and 125–139 in males, 26–31 subcaudals in females and 34–39 in males, 159–170 ventrals plus subcaudals in females and 161–174 in males, 9 maxillary teeth, anterior tip of the maxilla toothless, an overall dark dorsum, a predominantly cream venter, and a short tail in males. A Bayesian phylogenetic analysis of mtDNA sequences of the cytochrome b and tRNA Trn genes, including representatives of the new species, G. carinosus , G. dubius , and G. juarezi supported the distinctness of the new species.

A bstract A new species of the colubrid genus Geophis is described from the Sierra Madre del Sur of Guerrero, Mexico. The new species possesses all of the diagnostic characters of the sieboldi group, but differs from all of the other species in the group by having dorsal scales arranged in 17 rows, 133–139 ventrals in females and 130–137 in males, 24–31 subcaudals in females and 34–39 in males, keeled dorsal scales on at least the posterior three-fourths of the body, apparently no apical pits, and a light nuchal collar in juveniles. The new species fills a gap in the distribution of the sieboldi group between Michoacán and Oaxaca, and is the first Mexican species of the genus reported to exhibit both a unicolor (uniformly dark) and a bicolor (with dark markings on a red background color) body and tail dorsal patterns, a polymorphism similar to that previously documented in few lower Central American species.