The four species of the C. truncorum-group are reviewed: Cylindroiulus truncorum (Silvestri, 1896), C. parisiorum (Brölemann & Verhoeff, 1896), C. bellus (Lignau, 1903) and C. arborum Verhoeff, 1928. Male gonopods and female vulvae of each species are fully described and illustrated. Non-sexual characters such as developmental stadia, numbers of segments and anal setae, and metazonital sculpture, are also discussed. A key to the species is given, and a new synonymy: C. costatus Verhoeff, 1941 = C. bellus (Lignau, 1903), is established. As an addendum, Julus luscus Meinert, 1868 is reconsidered, and a lectotype is designated.