Remarks on the nomenclature of the genera Ptychodus Agassiz, 1834 and Buffonites Sternberg, 1829 (Ptychodontidae, Chondrichthyes)

Ptychodus (Ptychodontidae, Chondrichthyes) is a widespread genus of Cretaceous durophagous sharks (Cappetta, 2012), mainly known by isolated teeth. The year in which this genus was established has been variably set as 1835, 1838 or 1839, according to diff erent authors (Brignon, 2015). This chronological uncertainty is due to the diff erent publication dates of either the plates or text descriptions of Ptychodus species in the monumental paleoichthyological treatise “Recherches sur les poissons fossiles” by Louis Agassiz (hereinafter “Recherches”). Agassiz’s masterpiece consists of fi ve volumes published in installments (“Livraisons”), along with supplementary sheets (entitled “Feuilleton additionnel”), over a span of eleven years (1833-1844; Brown, 1890; Everhart, 2013; Brignon, 2015). Such installments and supplementary sheets, separately published all over this long period, consisted of small sections of text or plates from diff erent volumes resulting in considerable confusion in establishing the correct years of creation of several names introduced in Agassiz’s opus. Unfortunately, the name Ptychodus is not an exception. The intricate nomenclatural history of Ptychodus and some of its species has been recently disentangled by Brignon (2015), who proposed a series of nomenclatural acts aimed to preserve taxonomic stability and maintain Ptychodus mammillaris Agassiz, 1835 as type species of the genus (type species by subsequent designation by Woodward, 1912). Whereas we substantially agree with the majority of Brignon’s (2015) changes, the aim of the present note is to clarify some aspects of the nomenclature of the genus.