[Neoselachii] Compagno, 1977 - modern sharks and rays see Cohort Neoselachii Compagno, 1977
   Order Hexanchiformes Compagno, 1973 - six-gill sharks
     Family Hexanchidae Gray, 1851 - cow sharks
       1 Genus Heptranchias Rafinesque, 1810 [monotypic]
       2 Genus Hexanchus Rafinesque, 1810
       3 Genus Notorynchus Ayres, 1855 [monotypic]