... In Cappetta (2012), this canal is described as the main lingual duct and the main labial duct, respectively. The Rajiformes, Squatina, Chlam ydoselachus, the Heterodontiformes, the Orectolobiformes, the Lamniformes, the Carcharhiniformes and Palaeocarcharias have only one such canal (Casier 1947a, b, c, Goto & Hashimoto 1976, Herman 1977, Thies 1983, Herman et al. 1988, 1992, Werner 1989, Welton & Farish 1993, Case 1994, Cavin et al. 1995, Delsate & Thies 1995, Case et al. 1996, Siverson 1996, Ward & Averianov 1999, Zhelezko & Kozlov 1999, Cunningham 2000, Underwood & Ward 2004b, Malyshkina 2006, Adnet et al. 2007, Adnet & Cappetta 2008, Consoli 2008, de Carvalho et al. 2008, Underwood & Ward 2008, Schmitz et al. 2010, Underwood & Cumbaa 2010, Cappetta 2012, Guinot et al. 2013b, Cook et al. 2014, Reinecke 2014. There are, on the other hand, more than one of these canals present in the tooth roots of the Pristiophoridae, Echinorhiniformes and the Hexanchiformes (Chabakov & Zonov 1935, Casier 1947a, b, c, Welton 1974, Herman et al. 1987, 1992, Cappetta 1990b, Kemp 1991, Smart 1995, Zhelezko & Kozlov 1999, Cione & Medina 2009, Adnet et al. 2012, Cappetta 2012, Kitamura 2013, Kriwet & Klug 2014, Trikolidi 2014. ...