Papposilenus, DeVries, 2019

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 : 1558-1560

Papposilenus gen. nov.

Type species: Cerithium suprasulcatum Gabb, 1873 . Oligocene, Dominican Republic. Species included: Cerithium suprasulcatum , Gabb, 1873; Potamides ormei Maury, 1917 ; Potamides infraliratus Spieker, 1922 ; Papposilenus utriculus sp. nov.

Diagnosis

Broadly convex spire. Three beaded spiral cords on later teleoconch whorls; beads quadrate, flattened. Varices and ventrolateral varix absent. Outer lip flaring, thickened. Columella without fold.

Description

Shell medium size, spire broad, weakly or moderately convex. Protoconch unknown. Sutures thinly incised, impressed. All whorls with three spiral cords, posteriormost cord strongest. Early teleoconch whorls with anteriormost cord beaded, other two cords beaded or not. Later whorls with all three cords beaded; beads quadrate, low or flattened, producing tessellated surface; posterior row of beds may be axially elongate. Spaces between beads aligned across spiral cords to form opisthocyrt axial groove coincident with growth lines; growth lines medially broadly sulcate. Varices and ventrolateral varix absent. Base with six or seven unbeaded spiral cords; cords closest to periphery with incipient beading. Outer lip thickened, flaring posteriorly, with groove emerging posteriorly and abaxially but without becoming a posterior canal. Anterior canal short, straight, excavated, twisted from an axial to transverse orientation, positioned well posterior to broad spatulate anterior margin of outer lip. Columella short, smooth; parietal area with moderately thick callus.

Remarks

Woodring (1959: 177) listed characters shared by Potamides suprasulcatus , the type species of Papposilenus gen. nov., and Potamides lamarckii , the type species of Potamides , namely, the absence of varices on the spire, the absence of a ventrolateral varix, and the presence of a broadened outer lip and twisted anterior canal. Woodring (1959) also noted characters not shared: the coarsely beaded sculpture and the thickened outer lip of P. suprasulcatus .

Woodring (1959, 177) included four Miocene potamidids in his ‘ suprasulcatus ’ group, but none resemble Papposilenus suprasulcatus , nor the Caballas Formation species of Papposilenus described below, nor Potamides , sensu Reid et al. (2008). Specimens of the Haitian Potamides roumaini Pislbry, 1910 have strong unbeaded spiral cords on all but the earliest spire whorls. Specimens of the Haitian Potamides caobasensis Pilsbry, 1910 are smooth on all whorls, except a prominent sutural ledge. Specimens of the Haitian Potamides tippenhaueri Woodring and Mansfield, 1924 have a keeled, unbeaded, posterior spiral cord on all whorls and two anteriorly situated beaded spiral cords. Specimens of Potamides matsoni Dall, 1913 , from the southeastern USA, have a relatively narrow spire and wide interspaces between several unbeaded spiral cords.

Potamidid taxa referred herein to Papposilenus had already been synonymised with Potamides suprasulcatus , including a Miocene species from Venezuela synonymised by Hedberg (1937) and Miocene species across the Caribbean and northern South America synonymised by Woodring (1959), including Potamides ormei Maury, 1917 ( the Dominican Republic and Colombia; Weisbord 1929), Potamides ormei var. infraliratus Spieker, 1922 ( Peru; Olsson 1932), and Potamides infraliratus ( Ecuador; Marks 1951). The discovery of Paleogene potamidids in southern Peru with broad spires and three coarsely tessellated spiral cords shows that the ‘suprasulcatus’ morphology spanned almost 40 million years while remaining restricted geographically to the Caribbean, northern South America, and north-western South America.

Etymology

‘ Papposilenus ’, the elderly incarnation of the drunken, bald, overweight tutor and drinking companion of Bacchus, the god of wine; referencing the short, stout, coarsely featured taxa assigned to this genus.

Occurrence

Lower Paleogene, Cuenca Member, Caballas Formation, East Pisco Basin, southern Peru; Miocene, Florida through the Caribbean and to northern Peru.