A surprisingly large number of European spider species have never been reliably rediscovered since their first description many decades ago. Most of these are probably synonymous with other species or unidentifiable, due to insufficient descriptions or missing type material. Here we discuss about 50 of these cases, declare some names as nomina dubia and establish the following new or re-confirmed synonymies: Agelena mengeella Strand, 1942 = Allagelena gracilens (C. L. Koch, 1841) syn. conf.; Anyphaena accentuata obscura (Sundevall, 1831) = Anyphaena accentuata (Walckenaer, 1802) syn. conf.; Anyphaena accentuata obscura Lebert, 1877 = Anyphaena accentuata (Walckenaer, 1802) syn. nov.; Araneus diadematus stellatus C. L. Koch, 1836 = Araneus diadematus Clerck, 1757 syn. nov.; Araneus diadematus islandicus (Strand, 1906) = Araneus diadematus Clerck, 1757 syn. nov.; Araneus quadratus minimus Simon, 1929 = Araneus quadratus Clerck, 1757 syn. nov.; Araneus quadratus subviridis (Franganillo, 1913) = Araneus quadratus Clerck, 1757 syn. nov.; Centromerus unctus (L. Koch, 1870) = Leptorhoptrum robustum (Westring, 1851) syn. nov.; Clubiona caliginosa Simon, 1932 = Clubiona germanica Thorell, 1871 syn. nov.; Coelotes atropos anomalus Hull, 1955 = Coelotes atropos (Walckenaer, 1830) syn. nov.; Coelotes atropos silvestris Hull, 1955 = Coelotes atropos (Walckenaer, 1830) syn. nov.; Coelotes obesus Simon, 1875 = Pireneitega pyrenaea (Simon, 1870) syn. conf.; Coelotes simoni Strand, 1907 = Coelotes solitarius (L. Koch, 1868) syn. nov.; Diplocephalus semiglobosus (Westring, 1861) nomen oblitum = Entelecara congenera (O. P.-Cambridge, 1879) syn. nov.; Drassodes voigti (Bösenberg, 1899) = Scotophaeus blackwalli (Thorell, 1871) syn. conf.; Erigone decens Thorell, 1871 = Hylyphantes graminicola (Sundevall, 1830) syn. nov.; Liocranoeca striata gracilior (Kulczynski, 1898) = Liocranoeca striata (Kulczynski, 1882) syn. conf.; Phlegra rogenhoferi (Simon, 1868) = Phlegra cinereofasciata (Simon, 1868) syn. nov.; Styloctetor stativus (Simon, 1881) = Styloctetor compar (Westring, 1861) syn. nov. and comb. nov.; Tapinocyba bilacunata (L. Koch, 1881) = Silometopus incurvatus (O. P.-Cambridge, 1873) syn. nov.; Theridion varians melanotum Strand, 1907 = Theridion varians Hahn, 1833 syn. nov.; Thomisus trigonus Giebel, 1869 = Pistius truncatus (Pallas, 1772) syn. nov.; Titanoeca psammophila Wunderlich, 1993 = Titanoeca spominima (Taczanowski, 1866) syn. nov. and comb. nov.; Xysticus paniscus L. Koch, 1875 = Xysticus lineatus (Westring, 1851) syn. conf.