Diplocephalus cristatus (Blackwall, 1833) is confirmed as a dimorphic species, having two morphs: cristatus and foraminifer. This view was first proposed by Georgescu (1969), but not supported in the literature. Diplocephalus foraminifer (O. Pickard-Cambridge, 1875), D. bicephalus (Simon, 1884), D. rectilobus (Simon, 1884), D. foraminifer thyrsiger (Simon, 1884) and D. arvernus (Denis, 1948) are here considered junior synonyms of D. cristatus (Blackwall, 1833). Diplocephalus bicephalus belongs to the morph cristatus, D. rectilobus, D. thyrsiger and D. arvernus to the morph foraminifer. A lectotype (♂) is designated for Diplocephalus bicephalus Simon, 1884; the paratype female of D. bicephalus was incorrectly identified and actually belongs to Dicymbium nigrum (Blackwall, 1834). Savignia harmsi Wunderlich, 1980 is another dimorphic species, with the two strongly differing male morphs: typica and cor.