A new species of Sipo Snake, Chironius (Serpentes: Colubridae), from the Yungas of Bolivia

A new snake of the genus Chironius is described based on external morphological characters and phylogenetic evidence. The new species occurs in Bolivia, both in the humid montane forests of the Yungas of Cochabamba and in Santa Cruz. It differs from all congeners in having 10 dorsal scale rows at midbody, an entire cloacal plate, keeled paravertebral rows, lightly colored lower portions of the supralabials, a yellow snout, a short hemipenis, and lacking postocular stripes, proximal enlarged spines on the hemipenis, and apical pits. Adults and juveniles have an emerald green background color. The new species is recovered as the sister taxon of C. leucometapus, which is known from the Amazonian slopes of the Andes between central Peru and northern Ecuador. We also provide an identification key to the species of Chironius with 10 dorsal rows at midbody.