Plesiothyreus, COSSMANN, 1888

PLESIOTHYREUS COSSMANN, 1888 View in CoL

Scutella Broderip, 1834: 47 View in CoL (in part; not Lamarck, 1816). Type species: Scutella crenulata Broderip, 1834: 48 View in CoL (Anaa, Tuamotu Archipelago, French Polynesia; three syntypes BMNH) [a probable junior synonym of Pileopsis cytherae Lesson, 1831: 387 View in CoL (Matavai Bay, Tahiti, French Polynesia; holotype or a syntype MNHN-IM-2000-32564)], by subsequent indication by synonymy under Scutellina Gray. View in CoL

Scutellina Gray, 1847: 168 View in CoL (not Agassiz, 1841; replacement name for Scutella Broderip, 1834 View in CoL ). Type species: Scutella crenulata Broderip, 1834 View in CoL by original designation.

Plesiothyreus Cossmann, 1888: 191 View in CoL . Type species: Capulus parmophoroides Cossmann, 1885: 198 ; pl. 8, fig. 2 (Eocene, Paris Basin, France; type unknown), by original designation.

Phenacolepas Pilsbry, 1891: 89 View in CoL (replacement name for Scutellina Gray, 1847 View in CoL ).

Scutulina Cossmann, 1912: 214 View in CoL (replacement name for Scutellina Gray, 1847 View in CoL ).

Cinnalepeta Iredale, 1929: 274 View in CoL . Type species: Patella cinnamomea Gould, 1846: 151 (New South Wales, Australia; holotype USNM 5837), by original designation.

Remarks: The Eocene type species Plesiothyreus parmophoroides closely resembles certain Recent shells in shape and ornamentation, including that of Plesiothyreus newtoni Sowerby III, 1894 . The close phylogenetic kinship among Pl. newtoni , ‘ Pileopsis ’ cytherae Lesson, 1831 (type of Phenacolepas Pilsbry, 1891 ) and ‘ Patella ’ cinnamomea Gould, 1846 (type of Cinnalepeta Iredale, 1929 ) leaves no doubt as to the synonymy of the latter two genera under the oldest Plesiothyreus Cossmann, 1888 ( Fig. 1). The synonymous relationship between Plesiothyreus and Phenacolepas has already been suggested from a conchological point of view by Christiaens (1989). Regardless, the family name Phenacolepadidae based on Phenacolepas remains in accordance with current classification (see ICZN Article 40.1).

This genus contains several extant species that are characterized by a large (> 8 mm), conical or capshaped shell. The ventral side of the shell has a row of denticles on a slightly raised keel along the apertural rim ( Fig. 5A, B; see also Cossmann, 1885: pl. 8, fig. 2; Christiaens, 1989: 21), although this feature is lacking in Plesiothyreus cinnamomeus and its junior synonym Plesiothyreus pulchellus (Lischke, 1871) . Masculine.