Caritodens demissa

• Distinguished by the strong concentric growth lines
• Possesses a large, anterior ear
• No anterior cardinal teeth
• Strongly developed comarginal ridges

• Pelecypod. Flattened valve in limestone showing concentric growth lines. Note broad left “wing”, shorter right “wing”. Entire Cincinnatian.

Fossils of Ohio (1996):

• Ornamentation comarginal only.
• The Upper Ordovician genus Caritodens is represented in Cincinnatian rocks by C. demissa (Conrad), a large species distinguished by auricles (large winglike extensions of the hinge), strongly developed comarginal ridges, and the lack of any radial ornamentation.

McFarlan (1931):

• (Under Pterinea demissa) Distinguished by the strong concentric growth lines and large anterior ear (Grabau and Shiner 1909, p. 419). Measurements of a typical specimen—hinge line 42 mm., beak to center of base along oblique umbonal ridge 37 mm., beak about one-third distance from the anterior end. Common in the Maysville and Richmond.

Foerste (1924):

• Nicolet River Specimen. Height 55 mm, length 58 mm along hingeline. Anterior lobe short, extending about 4 or 5 mm anterior to a continuation of anterior outline of body of shell. Posterior wing relatively long and acute, extending about 15 mm posterior to inner part of concave posterior outline of body of shell.
• Outline of shell varied with age. In the mature specimen here described the main axis of the body forms an angle of 65 degrees with hinge-line, but at an early stage of growth this angle began as 55 degrees and changed to nearly 75 degrees in latest stages, 65 degrees being the average result. In the same manner, the anterior outline of body, exclusive of wing, in mature specimen forms an angle of about 77 degrees with hinge-line, but at early stages of growth angle was nearer 66 degrees. At all stages of growth posterior margin was concave between body and posterior wing, but the form of posterior margin was concave between body and posterior wing, but the form of posterior outline varied considerably. At an early stage of growth, lower half of posterior margin curved slightly outward or was nearly vertical and angle made between lower margin of posterior wing and hinge-line approximated 45 degrees. With increasing age, posterior outline of body became more nearly parallel to anterior outline, finally surpassing same in its forward slope, until angle with hinge-line became 60 degrees. At same time, posterior angle of posterior wing became much more prolonged and acute, and retral angle between body and wing became deeper.
• This means that the shell accelerated in growth most in a direction parallel to axis of body during earlier stages and also along upper part of posterior wing. Growth was at least along upper half of anterior margin of the body, and at later stages it was retarded also along the retral angle.
• Thus it will be seen that small specimens appear so different form mature ones as to suggest their belonging to different species.
• In the Waynesville member, in the Nicolet River section, specimens of Pterinea demissa retaining the shell are not rare. Shell material forming left valve consists of two different substances. Main body of shell, forming all except surface film, is whitish in colour and mostly is about 1 mm in thickness, though some parts of some shells exceed even 2 mm. Outer chitinous film black. Ligamental area about 2.5 mm high and striated longitundinally. A lunate callosity faces interior of shell; its ends follow anterior and posterior outlines of upper part of main body of shell, and the narrowed crest of its arch rises to a level about 2 mm below the striated ligamental area. Below and anterior to beak are several obliquely vertical teeth. Posteriorly, only posterior end of lunate callosity has been observed.< /li>
• It was the writer’s intention to figure the interior of the Nicolet River specimens, showing in what respect they differed form typical Pterinea, as founded on P. laevis. Unfortunately the specimens, and also the drawings based on these specimens, were lost in the Dayton flood, in 1913, and none has been found since. In these circumstances, the term Caritodens, with P. demissa as a genotype, cannot be regarded as well established, and future discoveries must be awaited in order to definitely establish its dental structure.
• Caritodens. Pterinea was founded by Goldfuss on Pterinea lavis, a Devonian species from Nassau, Germany. This species has a broad, striated, ligamental area. Immediately below that area, interior of shell is thickened along an area whose inner outline is only moderately concave. Anteriorly, in front of apex of beak, three or four teeth incline diagonally upward and forward at fairly strong angles, and posteriorly there are two or three long linear teeth deviating but moderately from hinge-area.
• This type of structure not known to exist among Ordovician forms usually referred to Pterinea, certainly not in the case of P. demissa.
• Locality and Horizon. Nicolet River section, Lorraine, in the upper part of the Pholadomorpha zone (No. 8547).
• Type Specimen. P. demissa was described by Conrad from the Lorraine near Rome, N.Y., where it occurred in the lower part of the sandstones overlying the Lorraine shales.
• Canadian Specimens. In the Proetus zone, P. demissa occurs in the Nicolet River section, Chambly Canton, and near Hawthorne.
• In the Pholadomorpha zone in Nicolet River section, St. Hilaire, Weston, Streetsville, three-quarters of a mile south of Clay cliffs, and on the Bass Lake road southwest of Little Current.
• In the Sheguiandah formation it occurs a quarter of a mile south of Clay cliffs.
• In the Waynesville member it occurs on Snake island; in the Nicolet River section; at Huron river, St. Hilaire, Vars, Weston, Streetsville, Oakville, Clay cliffs, and at Kagawong falls. In the Kagawong member it occurs 3 miles southwest of Little Current, southwest of Indian Village, and 2 miles northwest of Gore Bay. In the fossiliferous layers of the Queenston red clay shales it occurs at several localities from 6 to 8 miles northwest of Meaford.
• General Distribution. In addition to the New York and Canadian localities listed above, P. demissa ranges through the Maysville and Richmond formations of Ohio, Indiana, Kentucky, Tennessee.

Foerste (1910):

• Pterinea demissa Conrad as identified from the Cincinnatian strata of Ohio, Indiana, and Kentucky differs from Pterinea laevis, the type of the genus in the absence of a well-defined longitudinally striated ligamental area. Along the hinge line a narrow linear portion is bent parallel to the general plane of the valves and then inward along the margin serving as an area of attachment of the valves but without any ligamental thickening or striation. No anterior cardinal teeth have been seen. The anterior muscular scar must be faint since it has escaped detection so far. Agreeing with Pterinea are the greater convexity of the left valve the low convexity of the right valve becoming flat or slightly concave ventrally in mature shells the well-developed ear and wing and the obliquity of the body. The posterior muscular scar is large but not sharply impressed. In the Whitewater bed west of Camden Ohio, the cast of both valves is marked along the line of junction between the body and the wing by a deep groove 12 mm in length in specimens 55 mm high. These grooves indicate the presence of a single prominent linear posterior tooth in each valve. A similar specimen was found in the Hitz layer at the top of the Saluda bed at Madison Indiana. Careful search among the numerous specimens of Pterinea demissa in the Arnheim and Waynesville beds has not failed to reveal similar posterior teeth on well-exposed interiors nor have any been found in specimens from the Maysville formation. Possibly the White water forms here described belong to a different species.
• Pterinea demissa appears to be a distinctly more primitive type than Pterinea laevis. This is true especially of the Maysville and lower Richmond forms in which the posterior lateral teeth appear to be absent. These earlier forms are here chosen as the type of the more primitive group for which the term Caritodens is proposed.

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