Species: Hebertella frankfortensis (Foerste, 1909)
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Map point data provided by iDigBio.
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- C1 Sequence
- Note: Common in the Paris bed, Drennan Springs in Henry County, and at Cyanthiana (=Lexington Limestone) in Harrison County.
- Bigby-Cannon and Catheys Formations, KY & TN Late Mohawkian sediments into Cincinnatian
Identification in Hand Sample
- Shell outline semielliptical; costae coarse, bifurcation rare
- Cardinal extremities rounded
- Sulcus narrow to wide, shallow, with relatively few costae (≤ 15) between inflection points
- Ventral interarea low, catacline
- H. frankfortensis is readily distinguished from H. subjugata by its more rounded shell, shallower sulcus, and relatively coarse costae with rare bifurcations
Hebertella frankfortensis from the McMillan Formation of Ripley, Ohio (OUIP 855)
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Wright & Stigall (2013):
Wright & Stigall (2013):
- Diagnosis: Small, sparely costellate Hebertella species with a rounded outline and low sulcus. Shell outline semielliptical; costae coarse, bifurcation rare; cardinal extremities rounded; dorsal and ventral valves inflated, evenly biconvex; sulcus narrow to wide, shallow, with relatively few costae (≤ 15) between inflection points; ventral interarea low, catacline; delthrium opening at a wide angle (≥ 40°); dorsal interarea low, apsacline. Emended from Foerste (1909).
- Remarks: Hebertella frankfortensis most closely resembles its sister species H. subjugata. Both are characterized by small size, a semielliptical outline, and rounded cardinal extremities, yet H. frankfortensis is readily distinguished from H. subjugata by its more rounded shell, shallower sulcus, and relatively coarse costae with rare bifurcations.
- Adult shell small for genus, rarely wider than 25 mm; outline transverse subelliptical to subround; cardinal extremities rounded, rarely a right angle or alate; ventral interarea curved and apsacline, doral interarea curved and apsacline, rarely orthocline. Low fold on brachial valve and shallow sulcus on pedicle valve in specimens longer than about 5 mm; fold and sulcus may be strongly developed on valves longer than 15 mm. Costae coarse, generally non-branching, ranging in number from 29 to 40 in valves shorter than 10 mm, number not closely corresponding to size; with size increase, costae per 5 mm across midline, 8 to 12 at 5 mm anterior to beak and 5 to 7 at 10 mm anterior to beak.
- Pedicle valve interior with pronounced muscle scars; adductors on double ridge, not enclosed by wide diductor scars. Length-width ratio of scar field ranges from about 1:1 to 1:5, increasing during ontogeny.
- Brachiophores bladelike, grooved on interior face, brachiophore supports converging to meet valve floor on either side of the cardinal process. Low notothyrial platform having prominent anterior edge. Curved fulcral area plates form floor for sockets. Cardinal process shaft thin, myophore usually crenulated, either small bulb or indistinguishable from shaft. Secondary thickening or cardinalia absent or minimum. Adductor muscle scars indistinguishable to faintly impressed on larger valves; all scars subelliptical, long axes oriented about 30 degrees to midline. Low median ridge extending from notothyrial platform to between scars, faint ridge rarely present between the posterior margin and adductor scars.
- A species characterized by the relatively short hinge line, with greatest width at, or a little anterior to the middle. Fold and sinus inconspicuous, visible only when viewed anteriorly. Plications usually simple, strong, 4-6 in 5 mm., anteriorly, about 40 in all, and more closely spaced laterally. Width commonly 15-20 mm., length 0.75-0.80 width, convexity about 0.5 width. H. frankfortensis is first introduced low in the Jessamine, recurring again near the top and has its best development in the Benson. Where the typical Woodburn is developed it is not common. It recurs again in the Cornishville member of the Perryville.
- Radiating plications usually simple, about 40 in number, occasionally increased by intercalation near the postero-lateral angles to forty-five. Hinge-line distinctly shorter than the greatest
Width of the shell; the latter is found either at or slightly anterior to the middle. Brachial valve almost evenly convex, the low, broad, median fold being almost imperceptible except when the
shell is seen from the anterior side. The broad, shallow, median depression or sinus of the pedicle valve frequently is much more conspicuous, although in some specimens it scarcely amounts to
more than a distinct flattening of the anterior part of the valve.
This flattenng usually does not extend nearer to the beak than one third of the length of the shell. The hinge-area of the pedicle valve is slightly curved, inclining outward, the beak rising distinctly above the level of that of the brachial valve. The largest specimens attain a width of one inch. Compared with Hebertell borealis, Billings, from St. Martins’s
Junction, near Montreal, Canada, the flattening of the median parts of the pedicle valve begin nearer the beak and the shallow median depression toward the anterior margin of the shell is a more constant feature. The result is a general flattening of the valve. The line of junction between the valves, when the latter are viewed from the front, is more sinous. The brachial valve is never distinctly flattened or depressed anteriorly, but frequently is elevated slightly, sa as to correspond with the more distinct median depression of the pedicle valve. The close relationship of this shell to Herbertella borealis is undoubted.
- Geologic position. Common in the Paris bed wherever typically exposed in Kentucky. The most northen localites occur at Drennan Springs in Henry County, and at Cyanthiana in Harrison County. It occurs also in the underlying Prasopora simulatrix or Wilmore bed, but here it is much less abundant, or is even comparatively rare.