Originally: Dalmanella fairmountensis, Formerly: Resserella fairmountensis
Map point data provided by iDigBio.
- C3 Sequence (Corryville)
- C2 Sequence (Bellevue)
Identification in Hand Sample
- Shell small, averaging 15 millimeters in width
- Transverse, subtrapezoidal outline
- Diductor pedicle muscle scars vary widely, from bilobed and divergent to those in which diductor scars completely enclose the adductors
- Well defined pallial sinuses usually present in the pedicle valve
Heterorthina fairmountensis from formation of County, () and from formation of County, ()
- Diagnosis: Transverse, subtrapezoidal outline; diductor pedicle muscle scars vary widely from bilobed and divergent to those in which diductor scars completely enclose the adductors; well defined pallial sinuses usually present in the pedicle valve.
- Discussion: This species was originally designated by Foerste (1909, p.216) with the following description: “Shell small, averaging 15 millimeters in width, but sometimes attaining a width of 18 millimeters. Shell usually wider posterior to the middle, the lateral edges more or less straightened, but converging anteriorly, suggesting a trapezoid rather than a semicircular outline; however, shells with subquadrangular and with semicircular outlines also exist. Pedicle valve with sides somewhat flattened and sloping away from a more or less distinct median axis of elevation; the latter is more distinct posteriorly but frequently reaches the anterior margin. Lateral margins of the muscular area divergent as far as the anterior margin of the second pair, between which there is a strongly reentrant angle as far as the anterior of the adductor impressions. The adductor impressions are oblong and occupy about one-fifth of the muscular area. Brachial valve flattened toward the lateral margins, but slightly convex on each side of the distinct median depression; the latter is narrow near the beak, but widens anteriorly and produces a distinct abrupt curvature in the outline of the shell when viewed from the anterior side. The strong and rather wide median elevation separating the adductor scars broadens posteriorly between the crurallates, and supports the cardinal process. The latter is divided by a median slit, and is often fairly conspicuous.
- Geological position: Fairmount beds. The types are from the quarries in the southwest part of Hamilton, Ohio, where it is abundant. It is much less common at New Trenton, and half a mile east of Dillsboro Station in Indiana. It appears to have a very restricted geological range.