Aaglaocrinus Webster, 1981 † (extant flag source)
Aaptotoichus Loeblich & Tappan, 1982 † (extant flag source)
Abagaqiella Wu, 1986 † (extant flag source)
Abathoceramus Heinz, 1932 † (extant flag source)
Aberisphaera Wan, 1991 † (extant flag source)
Aberroconcha Adamczak, 1961 † (extant flag source)
Abia Poletaeva, 1972 † accepted as Labiostrina Poletaeva, 1972 † (extant flag source)
Abichia Andrusov, 1907 † (extant flag source)
Abiella Ragosin, 1933 † (extant flag source)
Ablacomya Zittel, 1895 † (extant flag source)
Abolescus Tichomirova, 1968 † (extant flag source)
Abonnencius Morillas Marquez, Castillo Remiro & Ubeda Ontiveros, 1984 † (extant flag source)
Abothrodon Couto, 1944 † (extant flag source)
Abracrinus d'Orbigny, 1850 † accepted as Carpocrinus Müller, 1840 † (extant flag source)
Abrestheria Wang, 1981 † (extant flag source)
Abrotus Dolin in Dolin & Pritykina, 1980 † (extant flag source)
Abscondus Tichomirova, 1968 † (extant flag source)
Abtychus Waagen, 1870 † (extant flag source)
Abuhammadina Abd-Elshafy & Ibrahim, 1990 † (extant flag source)
Abyssotherma Brönnimann, Van Dover & Whittaker, 1989 † (extant flag source)
Acadolenus Sdzuy, 1967 † (extant flag source)
Acaeniotylopsis Kito & de Wever, 1994 † (extant flag source)
Acamposoceras Dollfus, 1904 † accepted as Acompsoceras Hyatt, 1903 † (extant flag source)
Acanothyia Pomel, 1872 † (extant flag source)
Acanthalepis M'Coy in Griffith, 1846 † (extant flag source)
Acanthaloma Conrad, 1840 † accepted as Leonaspis Richter, 1917 † (extant flag source)
Acanthalomina Prantl & Pribyl, 1949 † (extant flag source)
Acanthaspides Ivshin, 1956 † (extant flag source)
Acanthaspis Newberry, 1875 † accepted as Macropetalichthys Norwood & Owen, 1846 † (extant flag source)
Acanthaspongia M'Coy in Griffith, 1846 † (extant flag source)
Acanthatrigla Gaemers, 1984 † (extant flag source)
Acanthechinopsis Gregory, 1906 † accepted as Tetragramma L. Agassiz, 1838 † (extant flag source)
Acanthelia Wells, 1937 † accepted as Echinopora Lamarck, 1816 (extant flag source)
Acanthochirus Oppel, 1862 † accepted as Acanthochirana Strand, 1928 † (extant flag source)
Acanthochonia Hinde, 1884 † accepted as Ischadites R.I. Murchison, 1839 † (extant flag source)
Acanthochonium Ludwig, 1865 † (extant flag source)
Acanthocnemis Hawle & Corda, 1847 † (extant flag source)
Acanthocnemoides Zherikhin, 1977 † (extant flag source)
Acanthocoenia d'Orbigny, 1850 † (extant flag source)
Acanthocoenium Duncan, 1884 † (extant flag source)
Acanthoconia Sollas in Harmer & Shipley, 1906 † accepted as Ischadites R.I. Murchison, 1839 † (extant flag source)
Acanthoderma Agassiz, 1835 † (extant flag source)
Acanthoderma Agassiz, 1844 † (extant flag source)
Acanthodes Dybowski, 1873 † (extant flag source)
Acanthodesma Zittel, 1876 † accepted as Acanthodesmia Müller, 1857 (extant flag source)
Acanthodis Miller in Absolom, 1933 † (extant flag source)
Acanthodocrinus Yeltysheva, 1979 † (extant flag source)
Acanthoecites Dacqué, 1934 † accepted as Acanthaecites Rollier, 1909 † (extant flag source)
Acanthogramma Hawle & Corda, 1847 † (extant flag source)
Acanthograpsus Spencer, 1878 † (extant flag source)
Acanthograptus Lapworth, 1881 † (extant flag source)
Acantholarcus Tedeschi, 1895 † (extant flag source)
Acantholepis Newberry, 1875 † accepted as Eczematolepis Miller, 1892 † (extant flag source)
Acantholissonia Leanza, 1972 † (extant flag source)
Acantholithus Lindström, 1899 † (extant flag source)
Acantholoma Castelnau, 1843 † accepted as Leonaspis Richter, 1917 † (extant flag source)
Acanthonotos Sauvage, 1870 † accepted as Hemithyrsites Sauvage, 1873 (extant flag source)
Acanthophiceras Diener, 1916 † (extant flag source)
Acanthophoria Gorjanovic-Kramberger, 1895 † (extant flag source)
Acanthopleurus Egerton, 1841 † accepted as Acanthopleurus Agassiz, 1844 † (extant flag source)
Acanthopora Verrill, 1864 † accepted as Echinopora Lamarck, 1816 (extant flag source)
Acanthoporidra Davis, 1934 † (extant flag source)
Acanthorhaphe Ksiazkiewicz, 1970 † (extant flag source)
Acanthorhynchia Buckman, 1914 † accepted as Acanthorhynchia Buckman, 1917 † (extant flag source)
Acanthosphaerites Rollier, 1922 † (extant flag source)
Acanthospira Weller, 1914 † accepted as Acanthospirina Schuchert & Le Vene, 1929 † (extant flag source)
Acanthostoma Credner, 1883 † (extant flag source)
Acanthotnyropsis Kamyshan in Kamyshan & Babanova, 1973 † accepted as Acanthothyropsis Kamyshan in Kamyshan & Babanova, 1973 † (extant flag source)
Acanthotrichaphis Shaposhnikov & Wegierek, 1989 † (extant flag source)
Acanthotuberculatus Quednau, 1999 † (extant flag source)
Acanthuncus Kulicki & Szaniawski, 1972 † (extant flag source)
Acantoceras Pavlov, 1892 † (extant flag source)
Acastina Reed, 1927 † (extant flag source)
Acastocephala Shergold, 1966 † (extant flag source)
Acastopyge Tomczykowa & Tomczyk, 1970 † accepted as Acastopyge Tomcyzkowa, 1971 † (extant flag source)
Acathocardia Meek, 1876 † accepted as Acanthocardia J.E. Gray, 1851 (extant flag source)
Acathuncus Kulicki & Szaniawski, 1972 † (extant flag source)
Acbastaucrinus Sizova, 1979 † accepted as Floricyclus Moore & Jeffords, 1968 † (extant flag source)
Acclisina Tryon, 1883 † accepted as Aclisina Koninck, 1881 † (extant flag source)
Acenograptus Herrmann, 1885 † (extant flag source)
Acerotherium Kaup, 1834 † accepted as Aceratherium Kaup, 1832 † (extant flag source)
Acerrotrupa Yu & Wang, 1981 † (extant flag source)
Acervularia Lonsdale in Murchison, 1839 † (extant flag source)
Acestra Römer, 1861 † accepted as Opeamorphus de Laubenfels in Moore, 1955 † (extant flag source)
Acestrus Agassiz, 1845 † accepted as Acestrus Woodward, 1901 † (extant flag source)
Achaenodon Cope, 1874 † (extant flag source)
Achantoceras Parona, 1928 † (extant flag source)
Acheonus Dolin in Dolin & Pritykina, 1980 † (extant flag source)
Achiardia Duncan, 1880 † accepted as Dachiardia Duncan, 1880 † accepted as Solenastrea Milne Edwards & Haime, 1848 (extant flag source)
Achilleia Renz, 1913 † (extant flag source)
Achrochordocrinus Clark & Springer in Eastman-Zittel, 1913 † (extant flag source)
Achtiaria Borissiak, 1914 † accepted as Palaeotragus Gaudry, 1861 † (extant flag source)
Achylsopsis Fritz, 1968 † (extant flag source)
Achyrodon Owen, 1871 † accepted as Amblotherium Owen, 1871 † (extant flag source)
Acicularia d'Archiac, 1837 † (extant flag source)
Aciculina Vyalov, 1968 † accepted as Aciculella Vyalov, 1968 † (extant flag source)
Aciculina Deshayes, 1861 † accepted as Eulimella Forbes & MacAndrew, 1846 (extant flag source)
Aciculolenus Palmer, 1965 † (extant flag source)
Acidapsis Conrad, 1840 † accepted as Acidaspis Murchison, 1839 † (extant flag source)
Acidochilus Cossmann, 1909 † (extant flag source)