Bovicornu, Meyer, 1886

Cotton, Laura J., Janssen, Arie W., Pearson, Paul N. & Driel, Rens van, 2017, Pteropoda (Mollusca, Gastropoda, Thecosomata) from the Eocene / Oligocene boundary interval of three cored boreholes in southern coastal Tanzania and their response to the global cooling event, Palaeontologia Electronica 20 (3), pp. 1-21 : 15

Genus BOVICORNU Meyer, 1886

Type species. Bovicornu eocenense Meyer, 1886 , by monotypy (early Oligocene , USA) .

Discussion. Shortly after its introduction by Meyer (1886) the validity of the genus Bovicornu was denied by Dall (1892, p. 302), who considered both species introduced in that genus by Meyer (1886, 1887) to belong to the caecid (benthic) genus Meioceras Carpenter, 1858 . Dall’s point of view was followed, with doubts, by Cossmann (1912, p. 154-155), but rejected by later authors ( Collins, 1934, p. 212; van Winkle Palmer, 1947, p. 464; Hodgkinson et al., 1992, p. 24). Indeed, in Meioceras the shell wall is considerably thicker and its protoconch is utterly different, whereas in Bovicornu the shell is thin-walled and the larval parts agree with species of the pteropod genus Creseis . Zilch (1959, p. 49) followed Collins and included Bovicornu with a query in the cavoliniid pteropods, considering it a possible synonym of Euchilotheca Fischer, 1882 , which is also a creseid genus, but its type species, E. succincta ( Defrance, 1828) , shows only very faint traces of spiralisation. We agree with Hodgkinson et al. (1992) that Bovicornu should be considered an independent genus in Creseidae .

Bovicornu species demonstrate a certain resemblance with Hameconia edmundi Janssen, 2008 , described from the late Oligocene (Chattian) of SW France. In that species the bilaterally symmetrical shell has a curvature of c. 180°, but it is curved in one plain, not in a spatial spiral. The curvature is dorso-ventral, as is clear by the presence of lateral carinae. Its larval stage differs from Bovicornu in having separate protoconchs 1 and 2. Janssen and Maxwell (in Janssen, 1995, p. 164), Janssen (2008, p. 160) and Cahuzac and Janssen (2010, p. 111) included the genus Hameconia in the Sphaerocinidae family.