Abstract
Rhagophthalmus Motschulsky, 1854 is the most speciose genus in Rhagophthalmidae, distributed in the region encompassing South, East, and Southeast Asia. Here, we describe R.nanussp. nov. from the Houaphanh Province of eastern Laos, which represents the smallest known species in Rhagophthalmus and one of the smallest in Rhagophthalmidae. We compare it with the morphologically similar and geographically close congeners and provide a preliminary identification key to adult males of Rhagophthalmus species from mainland Southeast Asia. Additionally, we discuss the morphology and variability of male genitalia within Rhagophthalmus.