A major obstacle to phylogenetic and systematic study of the Class Bivalvia is inadequate knowledge of hundreds of obscure and poorly defined Paleozoic genera. This study provides redescriptions and modern illustrations of the type species for all Paleozoic nuculoid bivalve genera, which make up about 10 percent of the generic names proposed for Paleozoic bivalves. An attempt has been made to include all generic names proposed before 1964 with Paleozoic type species which show any evidence of phylogenetic relationship to Recent nuculoid bivalves, as typified by the genera Nucula or Nuculana. Sixty-four generic names are treated. Eight of these names are nomenclaturally invalid (objective synonyms, nomina nuda, or otherwise unavailable names), leaving 56 valid names for Paleozoic nuculoid genera. Original type specimens of the type species were located and redescribed for 39 of these 56 names. Topotypes or other conspecific specimens were used as a basis for redescribing an additional ten type species, and the remaining seven type species, mostly rare Asiatic or eastern European forms, are redescribed from the original descriptions and illustrations. Type species are designated for the first time for 4 generic names (Bicrenuh, Ledopsis, Myoplusia, Praearca), and lectotypes are first designated for 19 generic type species. Subjective considerations, including subjective synonymies, are omitted in an attempt to provide an objective foundation of facts for all future evolutionary and systematic study of nuculoid bivalves.