Two species of Alopoglossus (A. angulatus and A. meloi) were recognized to occur in the Guiana Shield lowlands, northeastern Amazonia. A third group of populations forming a distinct genetic lineage related to Alopoglossus avilapiresae was recently documented in the region. The Guiana Shield lowlands area also encompasses the type locality of Alopoglossus copii surinamensis (currently considered a synonym of A. angulatus). Aiming at describing a possible new species of Alopoglossus from the Guiana Shield and evaluating the taxonomic status of A. copii surinamensis, we analyzed variation in scutellation and morphometrics of the two nominal species of Alopoglossus occurring in the Guiana Shield and A. avilapiresae, which was recovered as the sister clade of the new Guiana Shield lineage, by examining 361 specimens from French Guiana, Brazil, Suriname, Guyana, Colombia, Ecuador, and Peru. Our results revealed a distinct combination of diagnostic characters that supports the description of specimens displaying the third Guiana Shield lineage as a new species. The new species is also distinct from A. copii surinamensis that we retain under a synonym of A. angulatus after examination of all species of the angulatus group and by considering updated diagnostic characters. The new taxon described here increases the total number of known species of Alopoglossus to 15.