The subfamily Dipsadinae contains about 22 genus of Neotropical fauna and 24 others considered incertae sedis, but with common characters to the Dipsadinae subfamily. The genus Dipsas, Sibon, Sibynomorphus and Tropidodipsas compose the Dipsadini tribe, which is considered a well-based monofiletic group. The tribe is characterized by snakes with a high degree of morphologic specialization, related to the way of feeding and to adaptations to the habitat. The Dipsas genus includes approximately 32 species, distributed from Mexico to South America, it is constituted by thin and elongated snakes, with short and prominent head, great eyes, vertical pupils and absence of mental groove. The species are visible variable in coloration, number of scales and others morphologic characters. This extreme variation has made it difficult to define the limits between the species and to interpret patterns of geographic variation. The great morphologic variation of characters in D. catesbyi and D. pavonina, associate to the difficulty to identify taxons and the lack of information on geographic distributions, justify the necessity of a detailed analysis of these species. For that, the present study was divided in two chapters. The first one corresponds to the analysis of the individual, sexual and geographic variation of D. catesbyi and D. pavonina and a comparison of characters between the two species. The second one corresponds to the analysis of the macrostructure of the cephalic glands in these two species, relating them with others taxons of Dipsadinae.
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