Ceraticelus vesperus Chamberlin & Ivie, 1939 is a Synonym of C. fissiceps (O. Pickard-Cambridge, 1874) (Araneae: Linyphiidae)

Summary Examined specimens of Ceraticelus fissiceps (O. Pickard-Cambridge, 1874) and C. vesperus Chamberlin & Ivie, 1939 were indistinguishable in diagnostic characters, apart from some variation in clypeal slope. Statistical analysis shows no geographic cline between putative species, but rather greater variability of this character in the western spiders. There was also variation among specimens within each putative species in degree of development of the tooth of the apophysis of the male palpal tibia. Ceraticelus vesperus is therefore synonymized with C. fissiceps, Ceraticelus fissiceps is redescribed, and a lectotype is designated. The role of online tools that allow curators to identify and compare their holdings is noted.