The Epicrates cenchria complex is endemic to the Neotropical region, occurring in mainland portions of Central and South America. The taxonomic status of the nine currently recognized subspecies (E. c. alvarezi, E. c. assisi, E. c. barbouri, E. c. cenchria, E. c. crassus, E. c. gaigei, E. c. hygrophilus, E. c. maurus, and E. c. polylepis), were evaluated based on external morphology, osteology, and hemipenis characters. Results obtained through quantitative and qualitative analyses support the recognition of E. alvarezi, E. assisi, E. cenchria, E. crassus, and E. maurus as distinct species based on statistically robust delimitation of species boundaries.

In this paper I review the contributions of analytic and experimental research on intraguild predation and interspecific competition to our understanding of population regulation in plethodontid salamanders. Henry Wilbur's model of population regulation in amphibians serves as a framework for the arguments. Much of the discussion is based on studies of eastern North American plethodontids that have been the focus of most of the research. Ensembles of plethodontids in this region include species with complex life cycles (i.e., larval development) and simple life cycles (i.e., direct development). Interactions between members of these two life-history categories appear to be weaker than those within categories. Whereas there is no definitive evidence of factors that regulate populations of plethodontid salamanders, interspecific competition and intraguild predation do appear to contribute in some ensembles. Food and space have been identified as limiting resources in interspecific competition. Although predation of larger on smaller salamanders may be relatively rare in nature, the threat of predation appears to promote behavioral responses in members of the smaller species that reduce risks but may lower fitness through other effects. The role of extralimital predators and competitors in regulation of these salamanders is largely untested. Ideally, future research should involve manipulative experiments on unenclosed field plots that examine effects of resources, intraguild competitors and predators, and extralimital predators on populations of key species of plethodontids.

Seven species of Dipsas occur within Bolivia. On the basis of new material, we revise D. chaparensis, D. peruana, and D. variegata. We review D. i. cisticeps and consider it to be a subspecies of D. bucephala. We transfer D. boettgeri, D. latifrontalis, and D. polylepis to the synonymy of D. peruana. We consider D. neivai and populations of D. variegata from Bolivia, Brazil, and Peru to be conspecific with Guianan and Venezuelan D. variegata. On the other hand, we recognize D. trinitatis Parker as a morphologically distinct, full species rather than a subspecies of D. variegata. We refer Leptognathus robusta Müller to the synonymy of D. oreas rather than D. variegata. Alizarin red staining reveals calcification patterns of snake hemipenes and is recommended as a modification of techniques used to prepare these organs. Characters of visceral morphology improve our understanding of dipsadine relationships. As in most snakes, male Dipsas usually have higher subcaudal counts than females. On the other hand, species of Dipsas either have reverse ventral count dimorphism or their ventral counts are not dimorphic.

On the basis of new material from Colombia, we describe external morphology, the hemipenis, osteology, musculature, and visceral morphology of Tropidodipsas perijanensis, a species previously known from the unique holotype and long assigned to Dipsas. Tropidodipsas perijanensis may be the sister species of all other Dipsadini or the sister species of a clade formed by Dipsas and Sibynomorphus. This distinctive South American species cannot be assigned to Tropidodipsas or to any other genus, and we erect a new genus for it. Our study of cephalic musculature identified a previously unreported division of the m. levator anguli oris and new insertion of the m. intermandibularis posterior superficialis. New characteristics of dipsadine hemipenes were visualized by Alizarin staining. Some osteological characters of Dipsadini support synonymization of Sibon and most species of Tropidodipsas, whereas visceral characters and published molecular data suggest that Dipsas, Sibon, and Sibynomorphus form a clade.