Murchisonia aciculata (FOSSIL) J.W. Hall, 1860 †
Hormotoma aculeata (FOSSIL) Billings, 1866 †
Hormotoma acuminata (FOSSIL) Parks, 1915 †
Cheilotoma acuta (FOSSIL) (Münster, 1841 †)
Cheilotomona acutocarinata (FOSSIL) Tong & Erwin, 2001 †
Aclisina acutula (FOSSIL) (Dawson, 1868 †)
Hormotoma agilis (FOSSIL) Billings, 1865 †
Murchisonia akidota (FOSSIL) E.G. Linsley, 1968 †
Ostioma albanica (FOSSIL) Tassell, 1980 †
Coelocaulus alceste (FOSSIL) J. Perner, 1907 †
Murchisonia allevata (FOSSIL) J. Perner, 1907 †
Altadema altadema (FOSSIL) Mazaev, 2003 †
Hormotoma altesinuata (FOSSIL) E.F.R.K. Koken& J. Perner, 1925 †
Morania altevittata (FOSSIL) (Spitz, 1907 †)
Hormotoma amii (FOSSIL) McLearn, 1924 †
Murchisonia anderdoniae (FOSSIL) E.G. Linsley, 1968 †
Murchisonia anglica (FOSSIL) d'Orbigny, 1850 †
Crenulazona angulata (FOSSIL) E.G. Linsley, 1968 †
Murchisonia angulata (FOSSIL) (von Schlotheim, 1820 †)
Murchisonia angustetaeniata (FOSSIL) Paeckelmann, 1922 †
Hormotoma anna (FOSSIL) Billings, 1859 †
Hormotoma antigonishensis (FOSSIL) Peel, 1977 †
Hormotoma antiqua (FOSSIL) Peel, 1977 †
Catazone apate (FOSSIL) J. Perner, 1907 †
Murchisonia archiaci (FOSSIL) Paeckelmann, 1922 †
Murchisonia arctica (FOSSIL) (Tolmachoff, 1930 †)
Plethospira arenaria (FOSSIL) (Billings, 1859 †)
Catazone argolis (FOSSIL) J. Perner, 1907 †
Vebericochlis arguta (FOSSIL) Licharev, 1975 †
Hormotoma arisaigensis (FOSSIL) J.W. Hall, 1860 †
Goniospira armata (FOSSIL) (Münster, 1841 †)
Hormotoma artemesia (FOSSIL) Billings, 1865 †
Hormotoma articulata (FOSSIL) (Murchison, 1839 †)
Diplozone attava (FOSSIL) J. Perner, 1907 †
Morania attenuata (FOSSIL) (Lindström, 1884 †)