Cyclonema bilix

Phylum: Mollusca
Class: Gastropoda
Order: Euomphalina
Family: Platyceratidae
Genus: Cyclonema
Species: Cyclonema bilix (Conrad, 1842)

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  • 1842 Pleurotomaria bilix Conrad, Jour. Acad. Nat. Sci. Phila., vol. viii, p. 271.
  • 1842 Pleurotomaria bilix (part.) Hall, Pa. N.Y., vol. i, p. 305.
  • 1852 Cyclonema bilix Hall, Pal. N.Y., vol. ii, p. 89.

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Stratigraphic Occurrences

C. bilix_strat

Geographic Occurrences

Map point data provided by iDigBio.
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Sequences (Formations)

  • C6 Sequence (Elkhorn)
  • C5 Sequence (Whitewater, Liberty, Waynesville)
  • C4 Sequence (Arnheim)

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Identification in Hand Sample

  • Turbiniform, with height equal to or only slightly greater than width
  • Most common Cyclonema species
  • 2 to 4 whorls
  • 9-12 ridges occur on the exposed part of the upper whorls
  • Alternating strong and fine striae

Cyclonema bilix from unknown C5 sequence formation of Montgomery County, Ohio (OUIP 1896)

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Fossils of Ohio (1996) :

  • Cyclonema bilix is the most common species and has numerous fine, spiral costae of three different sizes on the whorls.

McFarlan (1931):

  • A turbinate shell, with height equal to or a little greater than width. Apical angle 55-75 degrees. Whorls 2 to 4, depressed convex, flattened or even a little concave centrally on the exposed outer part, with a shoulder-like convexity at both top and bottom giving a deeply impressed suture. Base of last whorl more or less flattened, narrowly rounded at the periphery. Surface with subequal revolving striae on the upper whorls, generally alternating on the body whorl, crossed diagonally by finer growth lines. These are exceptionally fine for the genus, about 12 in 2 mm. on the last whorl, 9-12 ridges occur on the exposed part of the upper whorls. On the body whorl about, 4 in 2 mm.

Ulrich & Scofield (1897) :

  • Shell subconical, the height and width equal, or the height may exceed the width by as much as one-fifth or in rare cases even one-fourth; apical angle varying from 55 to 75 degrees. Whorls generally three or four in number, the nucleus, consisting of three more, being absent in nearly every instance. In the typical form the whorls are depressed convex, flat or even a trifle concave in the central part of the exposed slope while at the top there is nearly always a small shoulder-like convexity which, with a similar convexity at the bottom, produces a distinctly impressed suture. Base of body whorl more or less flattened, narrowly rounded at the periphery; no umbilicus. Aperture oblique, somewhat triangular in a view of the base, subquadrate in a ventral view, the upper and inner sides of about the same length, and each about two-thirds as long as the lower side, while the outer side equals in length both the inner and upper sides; inner lip excavated, the excavated portion narrowly crescentic in shape, gently concave or straight on the inner side and strongly convex on the outer, usually 1.5 mm. across its widest part, rarely 20 mm. or more in old shells; inner margin of excavation sharp below, becoming more and more rounded toward the upper extremity where it turns sharply into the mouth. Surface marked by numerous, small, more or less regular revolving ridges and by much finer, sharply elevated, lines crossing the whorls from above obliquely downward and backward. On the outer surface of the upper whorls the revolving lines are mostly of the same size with from nine to twelve on each. On the body whorl where a new set is interpolated they generally alternate in size, with an average of ten or twelve in 5 mm. Of the oblique transverse lines, which run parallel with the margin of the aperture and are more closely arranged in this species than usual for the genus, the number in 5 mm. on the last whorl averages about thirty but varies between the extremes of twenty-five and forty. The last whorl of old examples usually exhibits more or less numerous irregular undulations and wrinkles of growth which generally cause some irregularity in the surface ornamentation.

Hall (1852) :

  • (Pleurotomaria bilix – Later renamed to Cyclonema bilix)Obliquely conical; spire short, composed of four or more volutions, which are somewhat appressed above and ventricose below; last volution somewhat flattened on the lower side ; aperture rounded, or slightly transverse; surface marked by numerous strong spiral carinae, which frequently alternate with finer ones; these are crossed by fine striae, which commencing at the top of the volution, pass obliquely backwards to the base, suffering no alteration of their direction upon the carinae (CONRAD).

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