Pleurorthoceras clarksvillense

Classification
Phylum: Mollusca
Class: Cephalopoda
Order: Orthocerida
Family: Orthoceratidae
Genus: Pleurorthoceras
Species: Pleurorthoceras clarksvillense (Foerste, 1924)

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1924 Orthoceras clarksvillense Foerste, p. 220, pl. 42, figs. 1A-B.
1932 Michelinoceras clarksvillense Foerste, p. 72.
1962 Pleurorthoceras clarksvillense Flower, p. 36, pl. 6, figs. 1-4.

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Stratigraphic Occurrences

Geographic Occurrences

Map point data provided by iDigBio.

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Sequences (Formations)

C6 Sequence (Elkhorn)
C5 Sequence (Liberty, Waynesville)

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Identification in Hand Sample

Narrow, subtubular, central to subcentral siphuncle segments
Slender, gradually expanding forms
Orthoconic longicones
Circular in cross section with straight, transverse sutures
Central siphuncle

Pleuorthoceras clarksvillensis from the Waynesville Formation of Waynesville, Ohio (OUIP 1545)

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Pojeta (1995)

Diagnosis. – Species of Pleurorthoceras distinguished by cameral lengths that range from one-half the diameter of the shell at diameters of 15 mm or less to one-third the diameter of the shell at diameters of 30 mm; narrow, subtubular, central to subcentral siphuncle segments one-eighth the diameter of the shell.
Description. – Medium-sized (lengths in excess of 65 cm and having shell diameters of up to 3.0 cm), slender, gradually expanding (apical angle of 4-5 degrees), orthoconic longicones; circular in cross-section with straight, transverse sutures. Cameral lengths decreasing with ontogeny from one-half the diameter of the shell at shell diameters of 15 mm or less to one-third the diameter of the shell at a diameter of 30 mm. Body chamber tubular, one-fourth the total length of the shell, aperture unknown. External shell surface smooth.
Siphuncle central in position at shell diameters of 15 mm or less, then becoming subcentral with ontogeny. Segments only slightly expanded, subtubular, the SCR values ranging from 0.285 (depressed) in adapical portions of the shell 15 mm or less in diameter to 0.33 (depressed) in portions of the shell 20-30 mm in diameter. Siphuncle segments narrow, from one-eighth to one-tenth the diameter of the shell. Septal necks short, suborthochoanitic. Connecting rings thin, homogeneous. Known portions of the siphuncle devoid of endosiphuncular deposits. Ventral mural deposits well-developed in adapical portions of large specimens at shell diameters less than 22 mm. Deposits becoming episeptal adapically with ontogeny. Adoralmost dorsal cameral deposits thin, mural.

Foerste (1924)

Specimen 130 mm. in length, consisting of 16 camerae, of which the uppermost is distinctly shorter, suggesting that the conch had reached full maturity. The specimen apparently enlarges from a diameter of 21 mm. at its base to 28 mm. at its top, indicating an apical angle of about 4 degrees. Near the base of the specimen two and a half camerae occur in a length equal to the diameter of the conch. Toward the upper part, three camerae occur in a corresponding distance. The sutures are directly transverse. The septa have a concavity of 5 or 6 mm. at mid-length of the specimen. The center of the siphuncle is located about one-third of the diameter of the conch from its central side. The segments of the siphuncle are cylindrical in form and their diameter is about 3 mm. along the entire length of the specimen. No part of the exterior shell remains, but the cast of the interior of the conch is smooth and it is possible that the exterior of the shell was smooth also.

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