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Species / Drepanocheilus Evansi


Chenopus (Drepanochilus) evansi in Cossmann, 1904, pl. VI, fig. 11, 12

History and Synonymy


Rostellaria americana Evans & Shumard, 1857:42


Drepanocheilus evansi in Sohl, 1960, pl. 11, fig 23, 26

  • image courtesy of the U.S. Geological Survey


Drepanochilus evansi Erickson, 1974, pl. 14, fig. 10, 11, 12, 13

Erickson, 1974, p.173:

  • "Drepanochilus evansi Cossmann, 1904. Diagnosis. Shell large for genus; body whorl strongly bicarinate, upper carina developing into long upturned pointed canal on flaring outer lip; lip becoming infilled and thickened in old age. Early whorls covered with threads crossing strong, almost evenly opisthocline ribs; on body whorls ribs are lost, seen only as nodes on upper carina, numerous small cords develop over body whorl as well. Pleural angle 25-30 degrees. Discussion. Because this is a common form from the Western Interior it has often been cited in the older literature and has thus developed an involved synonymy. It was a junior homonym of Rostellaria americana d'Orbigny a problem recognized and corrected by Cossmann in 1904 (p. 75) when he referred the species to Arrhoges (Drepanochilus) evansi, retaining Meek's (1864) subgeneric designation. Arrhoges as now used is a genus containing species with well-defined ribs on the last whorl and a blunt, broad outer lip to which D. evansi does not conform. It remains as the type of Drepanochilus which contains several Western Interior species that form a distinct evolutionary group in the midcontinent region. It was recorded from the Cannonball Formation by Stanton in 1921 (p. 37) and is not new to the state; Cvancara (1956) recorded it from the Fox Hills Formation. Types. - Hypotypes UND 13448, 893, 13455. Type locality. "Moreau and Grand Rivers" (Evans and Shumard, 1857, p. 42); this is in the type area of the Fox Hills Formation in South Dakota. Occurrence. D. evansi is common at two localities; from concretions in the Trail City Member at locality A469 and from fine and medium-grained sandstone of the Timber Lake Member at locality A460. Geologic range. Maestrichtian-Paleocene."

Specimens from institutional collections

Aporrhais americana (Evans and Shumard, 1857); Fort Pierre Beds, Cretaceous; Belle Fourche River, South Dakota, USA; Coll BMNH no. G. 10047

Drepanocheilus evansi Cossmann, 1904; Pierre Shale, Campanian, Cretaceous; Western Interior, Moreau River, South Dakota, USA; Coll. Yale Peabody Museum of Natural History YPM IP 008883


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