Orthonychiidae
Introduction †'''''Orthonychiidae''''' is an extinct taxonomic family of fossil sea snails, marine, gastropod mollusks in the clade Cyrtoneritimorpha.There is an unusually great degree of variability within the shells of species in the genus ''Orthonychia'', but an analysis of this variability has not been done yet (2008).
Genera Genus ''Orthonychia'' Hall, 1843*''Orthonychia acuta'' Roemer, 1856*''Orthonychia baldwini'' Rohr et al., 1981*''Orthonychia belli'' Clarke, 1908*''Orthonychia bowsheri'' Yochelson, 1956*''Orthonychia chesterense'' Meek & Worthen, 1866*''Orthonychia concavum'' Hall, 1860*''Orthonychia conicum'' Hall, 1860*''Orthonychia conoidea''  (Goldfuss, 1844)*''Orthonychia cornuforme''  (Winchell, 1863)*''Orthonychia costata''  (Barrois, 1889)*''Orthonychia daschi''  (Rohr & Smith, 1978)*''Orthonychia dentalium'' Hall, 1862*''Orthonychia enorme'' (Lindström, 1884) *''Orthonychia infabricatus'' Hyde, 1953*''Orthonychia marblecreekensis'' Talent & Philip, 1956*''Orthonychia obliquesulata'' Spitz, 1907*''Orthonychia pajerensis'' Chronic, 1949*''Orthonychia parva'' (Shumard & Swallow, 1858)*''Orthonychia parvulum'' Whiteaves, 1892*''Orthonychia pentalvea'' Talent & Philip, 1956*''Orthonychia perplexum'' (Hall, 1879)*''Orthonychia prosseri'' Clarke & Swartz, 1913*''Orthonychia protei'' (Oehlert, 1883)*''Orthonychia puellaris''  (Whidborne, 1891)*''Orthonychia quadrangularis'' (Whidborne, 1891)*''Orthonychia rostratus'' (Trenkner, 1867)*''Orthonychia sciotoensis'' Hyde, 1953*''Orthonychia sileni'' (Oehlert, 1883)*''Orthonychia subrectum'' Hall, 1860 - type species*''Orthonychia steinbergensis'' Kegel, 1926*''Orthonychia talon'' Tolmachoff, 1930*''Orthonychia tortuosa'' (Hall, 1860)*''Orthonychia trirotundolobatum'' (Talent & Philip, 1956)*''Orthonychia unguiculata'' Clarke & Swartz, 1913*''Orthonychia variablis'' Tyler, 1965*''Orthonychia vishtytica'' Saladzius, 1966*''Orthonychia vomerium'' (Winchell, 1863)*''Orthonychia waverlyensis'' Hyde, 1953* ''Orthonychia compressa'' / ''Platyceras'' (''Orthonychia'') ''compressum'' Girty 1910* ''Orthonychia ungula'' / ''Platyceras'' (''Orthonychia'') ''ungula''  (Weller, 1906)
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