Cyrtolites ornatus

Phylum: Mollusca
Class: Tergomya
Order: Cyrtonellida
Family: Cyrtolitidae
Genus: Cyrtolites
Species: Cyrtolites ornatus (Conrad, 1838)


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Stratigraphic Occurrences


Geographic Occurrences

Map point data provided by iDigBio.
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Sequences (Formations)

  • C5 Sequence (Whitewater, Waynesville)
  • C4 Sequence (Arnheim)
  • C3 Sequence (Mount Auburn, Corryville)
  • C2 Sequence (Fairview)
  • C1 Sequence (Clays Ferry/Kope)

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Identification in Hand Sample

  • Coil entirely in one plane
  • Final whorl out of contact with earlier whorls
  • Average shell
  • Surface with raised transverse lines and short connecting lines in alternating series
  • In the outer part of the last whorl there are commonly 7-8 of the transverse, and 8-9 of the short lines in a 2 mm span

Cyrolites ornatus from Fairview formation of Hamilton County, Ohio (OUIP 417, left) and McMillan formation of Kenton County, Kentucky (OUIP 790, right)

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Davis (1998):

  • Monoplacophoran. Coil in one plane. Final whorl does not contact earlier whorls. Note transverse ridges. Fairview – Waynesville.

Fossils of Ohio (1996):

  • Medium sized, its keeled shell is narrower than that of Sinuites, and it has broad, transverse undulations and a more loosely coiled shell.

McFarlan (1931):

  • Average shell 20-25 mm. in diameter, of 2 or 3 strongly carinated volutions, rhombic-subquadrate in cross-section, and rapidly expanding. Side subangular or narrowly rounded, the dorsal slope gently convex with strong transverse furrows and subangular ridges, the umbilical slope almost flat, without undulations. Ventral side with sharp, impressed zone. Umbilicus wide and deep. Surface marked by raised transverse lines with short connecting lines in alternating series. In the outer part of the last whorl there are commonly 7-8 of the transverse, and 8-9 of the short lines in 2 mm. There is no perceptible recurving of the transverse lines in crossing the dorsal carina.
  • Maysville and Richmond. A small variety, C. ornatus minor with a diameter not in excess of 11 mm. occurs in the Trenton of Minnesota and elsewhere.

Foerste (1924):

  • Shell distinctly carinated along the dorsum and very angular along the middle of the lateral sides. Intervening areas strongly plicated and striated transversely, neither plications nor transverse striae curving conspicuously backward on approaching the dorsum. Specimens from the Waynesville on Snake Island, and from the Pholadomorpha zone at St. Hilaire (Ontario and Quebec, Canada), have rather faint, short, oblique lines, at right angles to the transverse striae.
  • Locality and Horizon. Originally described from the Pulaski member of the Lorraine formation in New York. Widely distributed in the Maysville and Richmond formations from Canada, and New York to Alabama, from Ohio to southern Tennessee, and elsewhere. On Manitoulin island, a typical example (No. 8467), 25 mm. in diameter, was found at Clay cliffs, in the Meaford. Specimens occur also in the Lorraine in the Pholadomorpha zone south of Clay cliffs, and at McLean hill, 3 miles south of Little Current. At Weston, Ontario, it occurs in the Pholadomorpha zone. In Quebec, it is known in the Waynesville on Snake island and in the Nicolet River section. At St. Hilaire it occurs in the Lorraine in the Pholadomorpha zone, and at St. Hugues, in the Cryptolithus zone.

Ulrich & Scofield (1897):

  • Shell varying in diameter between 12 mm and 30 mm, with the average at about 23 mm. Volutions two or three, rapidly increasing in size, strongly and sharply carinate dorsally, rhombic subquadrate in section; sides prominent and subangular or narrowly rounded along a line about three-fifths of the height of the volution within the dorsal carina, the dorsal slopes gently convex and distinctly undulated by strong slightly curved transverse furrows and subangular ridges, the ventral or umbilical slopes almost flat and usually without undulations; ventral side with a sharp central furrow for the reception of the dorsal carina of the preceding volution. Umbilicus well defined, wide and deep, the edge wavy. Aperture a little wider than high, the height equaling usually a trifle more than half the greatest diameter of the shell, more or less rhombic-subquadrate, the outline often becoming a little rounded with age. Entire surface covered by a delicate network formed of raised lines running almost straight across the whorls and short connecting lines arranged alternately, the result being somewhat similar to the pitting of a thimble. In a good light the network is generally distinguishable without the aid of a magnifier, and, excepting three specimens, quite uniform in strength in different shells, there being on the other half of the last whorl nearly always seven or eight of the transverse lines and eight or nine of the short lines in 2 mm. In the excepted specimens the network is more compact, there being over the outer part of the last whorl from ten to twelve of the transverse lines in the same space. On another, with the reticulation unusually coarse, the number averages between six or seven. On the last specimen a good magnifier brings out some very fine lines of growth running through the network. It is important to note that there is no perceptible backward curvature of the transverse lines in nearing and crossing the dorsal carina.

Conrad (1838):

  • Shell with transverse rounded ribs and fine striae; peripherally acutely carinated.

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