Potamides Brongniart, 1810

DeVries, Thomas J., 2019, Early Paleogene brackish-water molluscs from the Caballas Formation of the East Pisco Basin (Southern Peru), Journal of Natural History 53 (25), pp. 1533-1584 : 1556

Genus Potamides Brongniart, 1810

Type species: Potamides lamarckii Brongniart, 1810 , by monotypy. Oligocene, France.

Remarks

Small cerithioids with a cancellate sculpture resulting from intersecting spiral cords and axial ribs or simply beaded spiral cords have variously been placed in Batillariidae or Potamididae ( Ozawa et al. 2009) . In the case of the two species described below, the presence of a columellar fold and the sharp abaxial bend of the anterior canal indicates placement with the Potamididae ( Ozawa et al. 2009) .

Reid et al. (2008) noted the difficulty of connecting the fossil and modern record of Potamididae and questioned the application of some names of extant genera to fossil species. Those authors restricted Tympanotonos Schumacher, 1817 to a single modern species and re-assigned Potamides conicus (Blainville, 1829) to Cerithideopsilla Thiele, 1929 , thereby rendering Potamides an exclusively fossil genus with a wider representation due to the inclusion of fossil taxa once assigned to Tympanotonos . Whether all such taxa are properly placed in Potamides awaits a more thorough study of the potamidid fossil record. Two taxa from the Caballas Formation are assigned to Potamides because they meet minimal criteria set forth for the genus by Reid et al. (2008): granular or tubercular spiral cords (three principal spiral cords with or without secondary cords), including an enlarged posteriormost spiral cord; a flared or thickened aperture; and an absence of varices, including the ventrolateral varix. A better assignment may be Pirenella Gray, 1847 , as more fossil potamidids are examined in light of recent studies ( Reid and Ozawa 2016) of Cerithideopsilla and Pirenella .

If spiral sculpture consisting of three or more beaded spiral cords is considered a diagnostic character for Potamides , several species from northern Peru attributed to Potamides should be reassigned: P. hondensis Olsson, 1931 , and P. chira Olsson, 1931 , both late Eocene or early Oligocene, and P. bocapanensis Olsson, 1932 , a smooth-shelled species from the Miocene. The Miocene species that Olsson (1932) named Potamides infraliratus Spieker, 1922 was subsequently synonymised with P. suprasulcatus (Gabb, 1873) and designated in this paper as the type species of Papposilenus gen. nov. (see below).