Subgenus Osilinus Philippi, 1847

Type species. Trochus turbinatus Born, 1778, SD, Opinion 1930, 1999). Present-day, Mediterranean Sea .

Diagnosis. As for Phorcu s. Umbilicus fully sealed. Callous columella with weak denticle.

Remarks. Conchologically nearly indistinguishable from Phorcus but the callus is a reliable character. It is broadly spread out in Osilinus but forms a rim, which may leave a chink or even an umbilicus in Phorcus .

Ravn (1933) and Lauridsen & Schnetler (2014) reported Osilinus carinatus Ravn, 1933 from the Danian (early Paleocene) of the North Sea Basin (Denmark). The illustrated specimen, however, is unrelated with Phorcus and Osilinus due to its low conical shell, large, inflated last whorl and wide umbilicus. This age would also be in strong disagreement with the molecular phylogeny of Donald et al. (2012), who assumed that the Phorcus / Osilinus lineage arose around 19–9.5 Ma.

Further records of the subgenus are allegedly reported from the early Miocene of the Proto-Mediterranean Sea ( Trochocochlea tauroparva Sacco, 1896) and from the middle Miocene of the NE Atlantic and the Central Paratethys Sea ( Phorcus (Osilinus) miocaenicus (Mayer, 1853) (Landau et al. 2003; Nosowska 2020). These species are umbilicate and lack any glossy circumbilical area as typical for extant Phorcus (Osilinus) species. In our opinion, they are unrelated with Phorcus (Osilinus) . Similarly, the two poorly preserved Pliocene species from the North Sea ( Trochocochlea erthensis Etheridge & Bell in Bell, 1893 and Trochocochlea littoralis Etheridge & Bell in Bell, 1893; see Harmer 1923) are most probably not closely related with Phorcus (Osilinus) . All these taxa are listed herein as Gibbula s.l.

No pre-Pliocene fossil records of Phorcus (Osilinus) are known.

= Caragolus Monterosato, 1884; type species Trochus turbinatus Born, 1778, SD (Crosse 1885: 440). Presentday, Mediterranean Sea.

= Pseudosilinus Nordsieck, 1974; type species “ Monodonta edulis Lowe, 1842 ” [= Phorcus (Osilinus) sauciatus (Koch, 1845)], OD (Nordsieck 1974: 21). Present-day. NE Atlantic. Remark. Monodonta edulis Lowe, 1842 is a nomen nudum and no such publication exists (Ávila et al. 2015) and therefore, Pseudosilinus is unavailable.

= Trochocochlea M̂rch, 1852; type species: Trochus turbinatus Born, 1778, SD (Bucquoy et al. 1885: 401). Present-day, Mediterranean Sea).

(Landau et al. 2003; Nosowska 2020)