Hydromorphus

Abstract: Newly collected material (26 specimens) of the snake genus Hydromorphus substantially extends the known variation in cephalic plates, chin shields, mental groove development, segmental counts and colouration. Variation in head shield seems to be associated with the semi-aquatic habits of these snakes. Variation in chin shields and a tendency for reduction of the mental groove may reflect a shift in diet from large to small prey items. Hydromorphus clarki Dunn, 1942, is placed in the synonymy of Hydromorphus concolor Peters, 1859; Hydromorphus dunni Slevin, 1942, from southwestern Panama is considered a valid species; H. concolor is recorded from Guatemala for the first time and ranges from there southward through Central America to central Panama. The latter species is oviparous.