A taxonomic revision of NW European Oligocene and Miocene Fasciolariidae traditionally included in the genus Streptochetus (Mollusca, Gastropoda)

A taxonomic revision is presented of Oligocene and Miocene species of the gastropod family Fasciolariidae from the North Sea, Paris and Mainz basins, previously assigned to the genus Streptochetus. No representatives of this group younger than Miocene (Syltian) have been encountered during this study. Four genera Fredenia gen. nov., Streptocarina, Streptodictyon and Streptolathyrus) are distinguished. Five new species are described: Streptodictyon impiger (Late Rupelian), S. schnetleri (Chattian B), S. twistringensis (Reinbekian), Streptolathyrus masculinus (Chattian A), and S. regularis (Hemmoorian). In addition, the following species are accepted: Fredenia ritzkowskii (R. Janssen, 1979) (Chattian A/B); Streptocarina klockenhoffi (Hinsch, 1977) (Syltian); Streptodictyon abruptus (Beyrich, 1856) (Reinbekian), S. cheruscus (Philippi, 1843) (Chattian-Hemmoorian), S. gottschei (Gripp, 1914) (Chattian B-Vierlandian), S. retrorsicosta (Sandberger, 1860) (Rupelian-Chattian A), S. sexcostatus (Beyrich, 1856) (Hemmoorian-Reinbekian), S. soellingensis (Tembrock, 1965) (Chattian A), S. sowerbyi (Nyst, 1836) emend. (Early Rupelian-Chattian A), S. subelongatus (d’Orbigny, 1852) (Early Rupelian), S. undatus (Meunier, 1880) (Rupelian); Streptolathyrus rothi (Beyrich, 1856) (Chattian B-Langenfeldian). Two taxa from the Rupelian had to be recorded in open nomenclature: Streptolathyrus sp. and Fasciolariidae sp. Type material was studied for several taxa; lectotypes are designated for seven taxa of the species group. Fusus dhondtae nom. nov. is introduced for Fusus Sowerbyi d’Orbigny, 1850, non Fusus sowerbyi Nyst, 1836 emend. Sexual dimorphism, suggested for this group of gastropods in the literature, could not be acknowledged. Some evolutionary trends are presented, but a cladogram was not constructed because of the impossibility to evaluate the relative value of morphological criteria.